Effect of Al doping on the martensitic transition and magnetic entropy change in Mn 50 Ni 40 Sn 10−x Al x was investigated. The experimental results show that the martensitic transition temperatures increase with the increase of Al content due to cell contraction, while the martensitic transition temperature range decreases rapidly. Mn 50 Ni 40 Sn 8 Al 2 alloy has the largest value of ΔSM (3.14 J/kg K) for the magnetic field changing from 0 to 10 kOe, which is nearly twice as large as that of Mn 50 Ni 40 Sn 10 alloy. It is demonstrated that a larger ΔSM can be obtained due to the sharper magnetization change around martensitic transition.