Low strength, which limits the industrial applications of Mg alloys, can be improved by forming Mg-based metal matrix composites (MMC) reinforced with ceramic particles. In this study, a Mg-based MMC was synthesized by introducing SiC particles into a WZ73 Mg alloy using the stir casting method. The effects of the SiC particles on the mechanical properties and corrosion behavior of WZ73 alloys were studied. The results showed that an addition of 1.5 vol % of SiC enhanced the strength of a WZ73 alloy but reduced the corrosion resistance. A further increase of SiC to 2.5 vol % had no effects on strength and corrosion behavior, which was attributed to the agglomeration of SiC particles. A microstructural analysis indicated that the addition of SiC did not alter the morphology and distribution of the secondary phase in the WZ73 alloy. Thus, the improved strength was attributed to the reinforcement of SiC and the refinement of the Mg grain, while the degraded corrosion resistance was the result of the grain refinement of Mg and the presence of the Mg/SiC interface in the vicinity of the secondary phase, which breaks the continuity of the Mg matrix and results in a higher corrosion rate.