Older cat playing too Rough with Kitten?

I have a 10 to 11 week old black cat. I had her for one day when I brought home a small Orange 6 Week old kitten. for the first few days the kitten didn't do anything but sleep. After that he started to come out of his shell and tried to play with the black cat. The black cat has always been nice to the small one, but when they play the black cat seems to aggressive with the little one. SHe'll put her mouth around the little ones throat, I dunno if she is bitting or what. THe little one lets out a scream, so I brek it up, and there fine. What's the deal?

You should have separated them right away especially if they haven't been vetted. The new kitten could be sick and you might not know it and putting the new one with the other one is not wise. You should have kept them separate and introduced them gradually over time, not all at once. I would put the new kitten away in a room with toys and a litter pan and food and water and make a vet appointment.

Agree that you need to have them both checked out at the vet before introductions.

Once they have their clean bill of health, you might want to separate them in adjoining rooms (they can see each other under the door). Find a game they both like, such as "chase the rope", and when you introduce them, get them both to play at the same time. If one sees the other enjoying the things that they like, the other usually realizes that the other is OK.

Worked with a couple of mine.