To investigate the effect of separate Al₂Ca and Mg₂Ca phases on the corrosion properties of Mg-Al-Ca-Mn alloys, OM, SEM, immersion and electrochemical tests were conducted on the as-cast and ECAP Al₂Ca-containing (2Ca) and Mg₂Ca-containing (4Ca) alloys. At the beginning of corrosion, the two as-cast alloys are corroded slowly compared with ECAP alloys. With prolonging the corrosion time, the corrosion of ECAP alloys becomes slighter than that of as-cast alloys, which is mainly ascribed to the dispersion and refinement of the second phase in ECAP alloys. Moreover, the corrosion degree of 2Ca alloys is always slighter than that of 4Ca alloys, suggesting that Al₂Ca phase is more beneficial to the enhancement of corrosion resistance of Mg-Al-Ca-Mn based alloys than Mg₂Ca phase. Finally, based on the examinations of corrosion surface and electrochemical testing results, different corrosion mechanisms caused by the distributions and morphology of Al₂Ca and Mg₂Ca phases are discussed.