Disclosed herein is supporting structure for an offshore wind power generator. The supporting structure includes lower support part and main body part. The lower support part includes lower concrete part which is provided on a base installed on the sea floor and is reduced in width from the bottom thereto to the top, at least one lower hollow space which is formed in the lower concrete part, and a lower inner-pipe which is attached to the inner surface of the lower hollow space. The main body part is coupled to an upper end of the lower support part. The main body part includes a main-body concrete part, at least one main-body hollow space which is formed in the main-body concrete part and communicates with the lower hollow space, and a main-body inner-pipe which is attached to a circumferential inner surface of the main-body hollow space.