Provided is an image decoding method including determining a current chroma block having a rectangular shape corresponding to a current luma block included in one of a plurality of luma blocks, determining a piece of motion information for the current chroma block and a chroma block adjacent to the current chroma block by using motion information of the current chroma block and the adjacent chroma block, and performing inter prediction on the current chroma block and the adjacent chroma block by using the piece of motion information for the current chroma block and the adjacent chroma block to generate prediction blocks of the current chroma block and the adjacent chroma block.