The surface modification of AZ91D magnesium alloy by laser alloying in which powder injection method was used for the purpose of improving the wear resistance of the alloy is evaluated. silicon powder was used as the feeding powder. The silicon powder reacts easily with molten magnesium to form fine Mg2Si compound in the modified layer. The wear resistance of the modified layer consisting of magnesium solid solution and Mg2Si compound was evaluated by conducting pin-on-plate type sliding test, and a satisfactory result is obtained. However, with large powder feeding rate and large amount of heat input by laser, a hard and brittle Mg-Al intermetallic compound crystallize so much in the matrix, resulting in the flaking of harder Mg2Si compound. Consequently, the Mg2Si compound drops out easily and the wear depth increases by ternary abrasive wear.