Methods and apparatuses for encoding and decoding based on intra prediction. The method of encoding an image based on intra prediction comprises dividing a current block into a plurality of sub blocks so that a plurality of unit blocks adjacent to each other are included in one of the sub blocks based on an intra prediction direction of each of the unit blocks included in the current block, and performing intra prediction encoding on each of the sub blocks so that only information about one intra prediction direction is encoded in each of the sub blocks.