Bringing a new baby home is always troublesome -- no matter if the baby is human or furry. Getting your older cat to accept the newcomer can also be problematic, but that doesn't mean it's impossible. A bit of patience and a trick or two is all it takes.
Step 1
Give the older cat places to hide from the new terror. Kittens are adorable -- but they are also annoying little creatures. They'll probably see the older cat as a new playmate -- although chances are the older resident won't agree. Make sure you provide a chance for your cat to get away when the kitten gets to be too much. This could be done in the form of open doors to other rooms or high furniture that a tiny kitten cannot jump onto just yet.
Step 2
Let them work it out in their own terms by taking it slowly. If you have an aggressive older cat and are worried, keep the kitty in a separate room for a while and just let the old resident to get used to the scent -- through the closed door -- at first. You can open the door after a couple of days, when both felines look and act more relaxed. Keep the interactions under control at first. For example, only allow the cats to be together when you're home to supervise. If you're leaving, lock them in separate areas of the house.
Step 3
Set up an additional litter box in a separate area of the house. Many cats don't like to share litter boxes, especially if they've been the only users for a long time. Show the new kitten the litter box he's supposed to use, but let him explore and try to use the other one as well. Some hissing is normal when cats are getting to know each other -- and especially if the older cat is trying to set some limits and rules. As long as no fights break out, the rest is just negotiation taking place.
Step 4
Give your older cat a lot of attention. Tons of it. One of the reasons he'll resent the newcomer is that he might feel displaced, so your job is to show him that he's still No. 1 in your life. If he likes to cuddle with you, make sure he's still able to without the kitten jumping all over him. If you need to sequester the new kitten in a different room to get quality time with your older cat, do so.
