The present invention relates to a video signal decoding method for adding an intra prediction mode as a sub-macroblock type to prediction of a macroblock in coding a video signal. The present invention includes obtaining a macroblock type, obtaining a sub-macroblock type when a macroblock includes a plurality of coded sub-macroblocks according the macroblock type, obtaining flag information indicating a DC (discrete cosine) transform size, determining the DC transform size of the coded sub-macroblock based on the flag information, when the sub-macroblock is intra prediction coded based on the sub-macroblock type, determining a prediction size of the intra prediction coded sub-macroblock based on the determined DC transform size, obtaining prediction direction information from a block adjacent to the sub-macroblock based on the prediction size of the sub-macroblock, and obtaining a prediction value of the sub-macroblock based on the prediction direction information. Accordingly, the present invention is able to raise coding efficiency of video signal by adding an intra prediction mode as a sub-macroblock type in predicting a macroblock.