Adding a new member to your feline family is usually more exciting for you than your current cat. Even though they are solitary by nature, most cats eventually learn to accept or at least tolerate newcomers. Because they are very territorial, way you go about introducing new cat to your existing cat can mean difference between success or "cat-astrophe."The introduction process can take as little as 10-12 days for kittens and very young cats, to as long as 12 weeks for older cats. It all depends on each cat's personality. Be sure to give your "first" cat plenty of attention. This will help him feel secure that he is not in competition for your affection.
Confine your new cat to a "safe" room until introduction process is complete. This should be a small room, such as a bathroom or small bedroom that your current cat rarely visits. Furnish it with a bed, scratching post, food, water and litter box.
In beginning, your first cat may hiss and yowl at cat on other side of door. Just ignore him and walk away. Never punish him for vocalizing aggressively, it will only cause trouble between two cats. Be sure to praise and pet your first cat when he acts calmly when near new cat's room.
After a few days, take a rag or washcloth and rub it over your new cat as you pet and play with her. Use a different rag to do same thing with your first cat. At feeding time, put each cat's scented rag under other cat's bowl. This will help them associate other cat's scent with something positive-food. Lots of little feedings each day will help them get used to smell more quickly. Be sure to renew scent on rags each day.