A method and apparatus for converting a resolution of a block-based image. The method includes: dividing a low resolution image frame into a plurality of blocks, each block having a predetermined size; performing motion prediction in a sub-pixel unit of each of the divided blocks and determining a motion vector in the sub-pixel unit; dividing the motion vector of the sub-pixel unit into a first motion vector having an integer pixel unit and a second motion vector having the sub-pixel unit; determining at least one low resolution reference block corresponding to each of the divided blocks by using the first motion vector having the integer pixel unit; converting each of the divided blocks into high resolution block by using the second motion vector having the sub-pixel unit and the one low resolution reference block; and generating a high resolution image frame by using each of the converted high resolution blocks.