Whether you are introducing a new cat to your resident feline or are dealing with some animosity between your existing cats, you can take steps to make everyone get along peacefully. Keep in mind that relationships between cats take time to develop. With a slow introductory process and some changes to your kitties' environment, your felines may become friends or at least tolerate each other in time.
Gender and Age Matches
There are a few things you can do to help ensure that your feline friend's new companion will be a good fit. If you have an adult cat, add a new kitten to your family, who your existing cat won't view as a threat. Choose a kitty with a similar temperament to your other cat. Litter mates tend to get along well, so adopting a pair of kittens will ensure that they'll be friends for life. Consider adopting two unrelated kittens together because younger cats are most open to forming bonds with other felines.
Cats of the opposite sex may get along better than pairs of males or females. Remember to spay or neuter all cats in your home to prevent unwanted kittens and fights for dominance between them.
The Introduction Process
When adding a new feline family member to your household, keep the new arrival in her own room, away from your resident cat. After getting her checked out by a vet, allow each cat to spend time in the other's space to get accustomed to each other's scent. Feed the kitties on either side of the closed door to the new kitty's room. Place a baby gate in front of the room, open the door and let the cats meet each other through the gate. When no one is hissing or growling, give the cats each some treats. Eventually, allow them to meet for a few minutes at a time, giving each cat some treats if they behave in a nonaggressive manner. Increase the amount of time they spend together during each visit.
Adjusting the Environment for Multiple Cats
Cats tend to be territorial, especially when it comes to important resources like food, water and litter boxes. Prevent spats among your cats by giving each cat her own litter box in separate locations, plus one additional litter box. Set up a feeding spot for each cat, giving each her own bowl for food and for water. Provide plenty of cat trees for the felines to climb and cat beds when they each need some alone time. When playing with the cats, give each one an individual interactive session with you so they get plenty of exercise and attention. Avoid playing favorites and give both pets equal amounts of attention. Occasionally treat them in each other's presence to reinforce good feelings between them as well.
Dealing with Issues
If one of your cats recently started to react aggressively, she could be suffering from an illness that is making her feel grumpy. Bring her to the vet for a checkup. Place plug-ins filled with synthetic feline pheromones around your home to promote a sense of well-being for your kitties. Provide all of your cats with plenty of toys to keep them busy during the day. If your feline friends are fighting or one is bullying the other, separate them and begin a slow reintroduction process again, as if they are first meeting each other. Don't leave your cats unsupervised together until they show no signs of aggression around each other, including hissing, swatting, growling or biting.