The dry sliding wear behavior of magnesium-matrix-composites (MMC) reinforced by boron carbide particulates (B4CP) has been investigated. Magnesium is the lightest structural material and is a good choice as a metal matrix for boron carbide and silicon carbide addition. Magnesium and its alloys, without reinforcement, are generally not suitable for mechanical applications due to their low wear resistance. The MMCs used in this study were produced via highpressure die-casting technique. The wear resistance of B 4C/AZ91D composite reinforced with 12 and 25 wt% B4C were studied, compared with unreinforced diecast AZ91D. As-cast microstructures of the materials and boron carbide particules were characterized by using Scanning Electron Microscopy (SEM). The hardness values of the control sample and the composites were determined via Vickers hardness measurements. Pin on disk dry sliding wear tests were carried out to study wear rate and wear mechanisms. The magnesium matrix composites were used as pins while mild steel as disc material. The worn surfaces of pins were examined by using SEM. The wear performance of magnesium matrix composites was improved with increasing volume fraction of B4C up to a certain level.