The British actor, who plays Edward Cullen in the film franchise, is worried film bosses will slap a restrictive rating on the two Breaking Dawn movies after considering them too extreme for teenagers.
He tells Entertainment Weekly magazine, "There's some interesting and weird stuff going on - really very, very, very strange. It's great. For a big mainstream movie, it's the most obscure storyline and really outside the box.
"It's a horror movie. I've seen a few bits, and I just can't see how it's going to be (rated) PG-13... unless they cut everything out."
The climactic scenes include the graphic birth of a vampire baby.