A method and apparatus for encoding and decoding an image based on intra prediction are provided. The method comprises predicting an intra prediction direction of a current block based on an intra prediction direction of a reference block located at an Nth pixel in the x-axis and an Mth pixel in the y-axis with respect to the current block, and intra prediction encoding the current block based on the actual intra prediction direction of the current block and the predicted intra prediction direction of the current block. Accordingly, the compression rate of image data can be improved by accurately predicting the intra prediction direction.