which university is biggest in world?

Answer 1

Probably the University of South Africa "with a total student body (formal and non-formal) in the region of 250,000."

http://www.unisa.ac.za/default.asp?Cmd=ViewContent&ContentID=3

The largest university in the U.S. is Arizona State University, with a total enrollment of 51,612 for Fall 2005.

Update: Actually, scratch University of South Africa, as that counts all their campuses. If multiple campuses count, then Indira Gandhi National Open University is the largest with 1.4 million students. But without counting multiple campuses, then so far, Arizona State University is the largest.