My cats hate each other!?

Cats are territorial and do not like change. Proper introductions must be done when introducing a new cat into the home.

Keep the kitten in a room by itself for at least a week if not more(get a vet check as well) your cats will get to know each other from under the door. Then take an unscented towel and rub your current cats scent on it and give it to the kitten. Repeat this process with a different towel except rub it on the new kitten and give it to your current cat to smell. Once you see them acting positively towards each others scent you can begin slow and controlled introductions. Expect hissing, growling and fighting this is all normal. Feed them around each other, play with them around each other, etc...let them experience good things when they are around each other. Eventually you can make introductions longer until you feel they can be trusted around each other.

If neither are spayed and neutered get that done as well it will help.

Well this is normal. You have to understand your bringing another cat/kitten into their territory. Also if she's hissing she might want to be the leader of the pack. You can tell when she tries to stand tall and also when they become better friends the adult eats first if they're eating out of one bowl. Don't worry I have had to introduce cats to other feline members of my family. It all works out. I'm guessing she's only been in the house for a few days? Introducing them right away is a big no no. The cat is scared to death already and doing it too soon will make matters worse for both of them. Keep the cat in a bedroom give he/her a food bowl, water bowl, plenty of space, litter box, and a place to hide when she feels threatened. Bring the other cat's toys into the room and/or other belongings to let the cat get familiar with her scent. You can put each cat on a other end of the door to let them sniff each other. Put the cat in another room and let the kitty out to explore the house. This may take some time because cats like to explore every possible crack and crevice. Then when you feel the time is right slowly introduce them or put one of them in a cat travel bag so one of them can sniff the other. There will very likely be growling and hissing involved as that is normal. Best of luck to you! Hope I helped!

It will take some time for your older cat to adjust. She may never like the new kitten but will learn to tolerate. Buy a cat condo so that the older cat can climb up and feel that she has her own space. Remember, you brought a stranger into HER house and she is not too happy right now. Give it time.

This happened when i brought home a new kitten.. But over time they get along now.. I had to keep them seperated for a week so that the old cat could smell the kitten but not hurt her.. I used a dog crate to keep the kitten in at night and stuff when we weren't around.. after a week i let her roam and they were fine after that..

Put them into gladiator death match,, lol jk is probably cause the old cat feels jelous of the new one it feels like is going to take away his territory