This study investigates dry sliding wear behavior of as-cast AZ31B magnesium alloy using a pin-on-disc type wear apparatus against EN42 steel with heat treatment as counterface. A wear mapping approach has been undertaken to represent the wear regimes and the main mechanism of wear in each regime. Wear resistance of as-cast AZ31B magnesium alloy was tested using pin-on disc method with heat-treated high-carbon steel discs as counterface on dry-sliding conditions. Wear tests at a fixed sliding distance of 2500 m were performed in sliding velocities of 0.25, 0.5, 1 and 2 m/s, loads of 10, 20, 40 and 80 N. Microstructural examinations of worn surfaces of pins were characterized using SEM/EDS. Wear mechanism map of investigated material was drawn. The main wear mechanisms in each test conditions were identified and classified using the wear mechanism map. Three wear regimes, namely mild wear, severe wear, and ultra-severe wear were defined, based on the results. Consequently, ultra-severe plastic deformation is the main wear mechanism at the highest applied load and sliding velocity speed.