The corrosion of a magnesium-based MMC, comprising a ZC71 alloy matrix and 12 vol% silicon carbide particles, has been studied in saline environments, using salt-spray and electrochemical tests. Corrosion was localized initially, and developed subsequently into general corrosion, the local corrosion rate being about three times faster than that of conventional ZC71 alloy due to the formation of less protective corrosion products. Galvanic corrosion, due to coupling of the matrix and reinforcement, and the formation of reactive phases at the matrix/reinforcement interface were not significant factors in the corrosion of the MMC.