It is about a green monster, called mike I think, and he has black hair, horns, and he wears jeans and a leather jacket.

He takes the kid under the bed and shows him the underworld of the monsters.

Right at the end of the film, the monster gives the kid his leather jacket.

Please help me!!

This sounds like "Little Monsters" (1989). In it a boy, played by Fred Savage (from The Wonder Years and Austin Powers Goldmember), meets all these monsters under his bed, becomes friends with them, and plays tricks on people with the help of the monsters. The monster he first meets does have black hair and horns, but I remember his skin being purple and his name was Maurice not Mike. He was played by Howie Mandel. I really liked this movie as a kid. You can read more about it here and see if it's the movie you're looking for:

http://www.imdb.com/title/tt0097758/

Cheers mate, and thank you for correcting me. I will see if I can find it. Cheers mate

We here in glasgow think it could be Monster Inc other than that we are not too sure sorry

tyieka

Hi again mug101. Last night I saw a copy of Little Monsters for sale on DVD, for a very reasonable price... so hopefully you won't have any trouble finding it. Plus, Maurice's skin was BLUE on the cover of the DVD, so I guess we were both wrong. ;) Anyway good luck!

I agree with orange, the movie you're talking about has got to be Little Monsters. You should be able to find it easily in any video rental store under "comedy", maybe "family".