Provided is an adaptive motion search range determining apparatus and method for encoding UHD-class high-resolution images. The adaptive motion search range determining apparatus includes an MVD average/standard deviation calculation unit calculating an value average and a standard deviation of MVDs of neighboring macroblocks of a current macroblock, and a motion search range determination unit determining a motion search range of the current macroblock using the value average and the standard deviation. According to the adaptive motion search range determining apparatus, it is possible to enable each macroblock to have an adaptive search range by variably adjusting a motion vector search range of a current macroblock with reference to motion vectors of neighboring macroblocks of the current macroblock.