It is well known for us that prohibiting riba is one of basic elements in Islamic economic theory and finance besides prohibiting Gharar(uncertainty) & Qimar(gabling), conformity with Sharia and profit & loss sharing. We've gotten used to understanding all kinds of riba was prohibited in the early islamic history by Quran and Hadith. But we don't know well a kind of riba was first prohibited by Quran and other kinds were prohibited by Hadith in the 7th years from the Hegira. It is very curious what made difference in time and way for prohibiting riba. If we knew the historical situation of arabian peninsular in that time, we are surely going to understand why there should be time difference in prohibiting some kinds of riba, and how many kinds of riba were classified in the islamic financial and commercial transactions. This research tried to demonstrated why and how Islam prohibited riba and be useful to set the basis of islamic economic and financial theory.