When we think of “aggression,” we may think of a variety of motivations and impulses deriving from our own experience as humans. Fortunately, aggression in cats is easier to make sense of and typically derives from two impulses: fear and mistrust. These are the most likely scenarios to cause fear and mistrust amongst cats:

  • One or more cats in the home are intact (not spayed or neutered).
  • A new cat recently entered the home.
  • Long-standing tensions between two or more resident cats.
  • A source of stress in the home creates tension amongst cats who previously got along.
  • A one-time event triggers two cats who previously got along.

The good news is that cat owners can reduce their cats’ fear and mistrust of each other and increase positive feelings among the cats in the household.

But before moving to the specifics, let’s address three words that you’ve probably heard before: “Cats are territorial.” But what does this actually mean? Well, let’s start with dogs. Dogs are scavengers by nature—they go where the food is—and while they may guard certain objects or spaces, they are not territorial in the way cats are.

Cats, unlike dogs, are hunters by nature and, also unlike dogs, they don’t wander from their territory. To go outside their territory puts cats at risk of encountering other cats and other animals who they are competing with for food and who may potentially harm them. On the other hand, a new cat entering the resident cat’s territory is likely to be perceived as a potential threat.

Related to being territorial is the need for cats to feel safe and secure in their territory—knowing that they are not in danger and that all resources they need to survive and thrive are readily available. A cat who does not feel safe and secure in their territory will hide or may show aggression in an attempt to keep potential danger (other cats) away from them.  

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With these ideas in mind, here are the steps to resolve—or, better yet—avoid aggression between cats:

Spay or neuter your pets.

Spaying and neutering greatly reduces aggression in cats. More to the point, because of their impulse to be territorial it’s often impossible to resolve aggression among cats if one or more cats is intact.

Introduce cats slowly.

Slowly means at the pace of the cat who is showing the most fear and mistrust. This may be the new cat or the resident cat(s). This pace may be a matter of days, weeks or months—it's up to the cat. The role of the cat owner is to provide an environment that increases the likelihood of the cat feeling safe and secure in the new territory and/or with the other cat while moving at the cats’ pace. It’s important to understand that cats do not “work things out.” If cats are not getting along the tensions will only increase unless the proper introduction or reintroduction is taken.

Introducing Your New Cat to Other Pets

Make sure there are enough resources in the home to avoid feelings of mistrust and competition.

A resource is anything the cat needs or wants. For example: litter boxes, scratching posts, food/water bowls, human attention and play time, resting spaces, hiding spaces and toys.

Make sure everyone is getting enough play time.

One cat (typically the younger, active cat) chasing the other cat in play is often perceived as aggression when it’s actually a result of the cat not having their daily energy needs met. Cats have much more energy to expend than most of us realize. If we are not proactive in meeting our cats’ energy needs, the more active cat may chase the less active one (fun for the active cat, but not very fun for the less active one who just wants to be left alone). Play is also a great way to reduce stress in cats. When cats are playing, they think they are hunting and play can boost a cat’s confidence while also expending physical and mental energy.

Give the cats a reason to like each other.

To change the mindset of cats who fear/mistrust each other, give them a reason to like each other. What does this mean for cats? Providing them with something they love when the other cat is around or when they see the other cat. Typically, this involves giving the cats food or a treat! Play time, as well as grooming (assuming your cat likes to be brushed), can also lead to positive associations. It’s important to note that this is a process which may take a long time and requires consistency.

Be aware of any changes in the environment that could lead your cats to feel less safe and secure.

Cats are very sensitive to changes in their territory and if they feel less safe and secure in their home this may indirectly cause tensions among the cats. For example, construction outside or inside the home, change in routine or the introduction of new people/other animals into the home (to name only a few possible stressors). When possible, take action to minimize the impact of these changes. 

Take your cat to the vet if you suspect they are ill or injured.

Ill or injured cats do not feel safe and secure and this can create tensions in a multi-cat household.

Contact a professional cat behaviorist if additional help is needed.

This is particularly important with a specific type of aggression called “redirected aggression.” This involves a single event that frightens one or more cats and, in this moment of fear, one attacks the other. A common example is if two cats are sitting on a windowsill and an outdoor cat appears which suddenly frightens the cats. A sudden loud noise or a sudden injury can also cause this behavior. It’s extremely important that the cats remain entirely separated until both cats are acting like their normal selves and then a slow re-introduction is needed. This process can be a challenge and is best done under the guidance of a professional.

What behaviors are "aggressive?"

Not all “aggressive” behaviors are the same. In fact, some cat behaviors often assumed to be aggressive are not.


A cat’s way of saying “leave me alone.” A cat who hisses is not feeling safe and secure in that moment. This is a defensive vocalization and a hissing cat will likely only go on the offensive if they continue to feel threatened and feel they have no other choice. When introducing cats, consistent hissing is the signal to the cat owner to slow the introduction process.


Another defensive vocalization and indicates the cat is feeling very unsafe and insecure.


A defensive behavior in which the cat is trying to create distance between themselves and the other animal or person.

Stalking and chasing

This behavior is very much based on the context. While chasing may be a result of territorial issues, sometimes it’s playful behavior (or at least perceived as play by the cat doing the chasing).


This behavior is a last resort for cats and is a result of either significant territorial issues and/or one or more cats feeling very unsafe and experiencing a great deal of stress. Contact a professional cat behaviorist if your cats are physically harming each other.