In a word, maybe. Male cats might accept another cat in your home or they might not; it depends on the situation. Throw two un-neutered males together, and chances are they will clash -- fighting or at least acting aggressively to each other regularly. If you control the environment carefully, you have a better chance of your male cat accepting another.
Un-neutered male cats often behave like two guys fighting over the same girl, or in archaic gang slang, their "turf." The motivation is usually the same: The toms want to show their brute strength through aggressive behavior to win the prize, the available lady cats. You can tell a fight is brewing when the cats stare each other down, howl, hiss, puff up their fur and arch their backs. A cat defending himself will crouch down, wrap his tail around himself and flatten his ears.
Cats are territorial animals, males more so than females. They make the rules and might accept one cat but not another. There is no way for you to predict whether your male will accept the new cat you bring home. Some cats share their territory and some won’t. The most unlikely pairings are two unrelated males or two unrelated females, so you might have a better outcome introducing a female cat to your male, especially one that is younger and smaller.
If your cat has not been around other cats much, he is unlikely to take kindly to another cat. Cats don’t particularly like change, and an undersocialized cat probably won’t welcome a newcomer on his turf. Cats that were socialized well as kittens with other cats usually are more willing to accept a new cat into the home.
Help Ensure Success
If you neuter your male before introducing him to a new cat, he will be more likely to accept the newcomer. Set up an area in the house for the new cat so each cat can have a place. Provide separate food and water bowls, and separate litter boxes. When you introduce the new cat to your male, and they look as if they will start fighting or if they do start fighting, break it up. The more they fight, the less likely they will be to ever accept each other after the new cat has become accustomed to his new arrangement. Clap your hands loudly, toss a pillow or spray them with water.
Put the cats in separate areas, but try reintroducing them later. Make sure you supervise them when you do. If they start to show aggression, separate them immediately. Keep trying at a gradual pace, and one day they might be the best of friends. Never leave them alone together unless you are sure they can get along.
- street cat gaze image by Maya Tairy from Fotolia.com