Mn-based Heusler alloys were selected as testing materials in this research, and the samples were prepared by arc-melting, subsequent heat treatment, and made in ribbon form by melt-spinning. The effects of Mn concentration on the crystal structures, magnetic and magnetocaloric properties were studied. It was found that Mn2-xSn0.5Ga0.5 crystalized in hexagonal structure at the room temperature. All samples undergo only second order phase transition at their Curie temperature near room temperature with nearly zero hysteresis. The Curie temperature and the saturation magnetization of the Mn2-xSn0.5Ga0.5 are very sensitive to Mn concentration where both Curie temperature and saturation magnetization decrease with the increase of Mn concentration, from 304 K and 64.1 emu/g to 262 K and 46.7 emu/g for Mn1.2Sn0.5Ga0.5 and Mn2Sn0.5Ga0.5, respectively, which indicates the ferrimagnetic order in these materials. Mn-based Heusler alloys will have a large application prospect in the field of magnetic refrigeration because of the absence of hysteresis and thermal hysteresis and with wide operating temperature range near room temperature.