The structural stability and magnetic properties of MnSUB3+x/SUBAlSUB1-x/SUBC antiperovskite with varied Mn/Al substitution were studied systematically. Single phase MnSUB3+x/SUBAlSUB1-x/SUBC alloys with antiperovskite structure were obtained in samples with x = −1/4, 0, 1/4, 1/2. An additional MnSUB23/SUBC₆ phase was precipitated from MnSUB3+x/SUBAlSUB1-x/SUBC antiperovskite for x = 3/4 while MnSUB23/SUBC₆ phase was formed as major phase for x = 1. The mutual substitution of Mn and Al atoms has substantial effect on the Curie temperature and the saturation magnetization of the MnSUB3+x/SUBAlSUB1-x/SUBC alloys. In comparison with the as-cast alloys, the as-annealed MnSUB3+x/SUBAlSUB1-x/SUBC alloys exhibit reduced Mn/Al substitutions after high temperature homogenization, which enhances the ordering of Mn and Al atoms in the lattices. The Curie temperature of the homogenized MnSUB3+x/SUBAlSUB1-x/SUBC increases with increasing Mn substitution to Al. The Mn₃AlC alloy shows the highest saturation magnetization among all samples with varied Mn/Al ratios. Most samples show zero coercivity and zero remanent magnetization. The maximum value of the magnetic entropy changes of MnSUB2.75/SUBAlSUB1.25/SUBC at 285 K is 2.26 J/㎏ K in fields up to 3 T.