Introducing a cat or kitten to another cat
Caring for two cats is just as easy as caring for one. They will entertain and exercise each other, and, most importantly, provide company for each other.
If you are already the guardian of a cat and want to adopt another, it is best to adopt one that is younger, smaller, and the opposite sex of the one you now have. Your older, larger cat will be more accepting of a younger, smaller cat. To avoid inter/male, inter/female rivalry, it is best to adopt the opposite sex.
To minimize the possibility of territorial spraying, all cats in the household should be neutered.
Before bringing your new cat or kitten home, take her to a veterinarian to get her wormed and vaccinated. Be sure to get her tested for feline leukemia. After the visit to the veterinarian, take her to a friend's house and give her a bath using an approved cat shampoo. Bathing not only removes fleas but also neutralizes all the other cat's odors which, when detected by your existing cat, will cause her to go crazy. Now your new cat or kitten is ready to go home.
There are two other ways of masking the odor of this new beast who is threatening the security of your existing cat's territory. You can either spray an inexpensive diluted perfume on both cats before the introduction so that they will smell alike, or you can rub a clean, damp towel on your existing cat. Then, using that towel, rub her odor on the new cat, and reverse the procedure with the new cat. They will be more accepting of each other if they smell the same or like themselves!
Next, confine the new kitty, for one day, to one room with her food, water, and litterbox. A litterbox is necessary because this new kitty should not go outside for at least three weeks, even if she is going to be an occasional outside cat. She needs a chance to become accustomed to her new home. If she is to be an indoor cat, then it is best to provide one litterbox per cat, anyway. During this one day confinement, the existing kitty will have a chance to smell and hear the new kitty. The following day, confine the existing kitty in the same room, and let the new kitty roam the house. The third day, let the two cats come together.
There will be some chasing, perhaps some hissing, and maybe even some minor fighting. Don't worry. Let them work it out! This behavior may last for three weeks or more. There may also be some spraying by the existing cat. Don't scold her. Just accept this adjustment period. Most cats learn to live together. It is very rare that two cats will not eventually get along. Once the cats have had a chance to get acquainted with each other, you can move their feeding stations closer together, but keep the litterboxes separated in an out-of-the-way quiet place.
From this point on, enjoy their antics and their companionship!