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Effect of Ta-alloying on microstructure, martensitic transformation, mechanical property and shape memory effect of Ni54Mn25Ga17.5Ta0.5 alloy has been systematically investigated. The results show that the substructure of Ni-Mn-Ga alloy significantly changed, which was converted from the plate martensite to the lath martensite. Compression tests show that a compressive strength of 1380 MPa with a fracture strain up to 21.92% can be achieved in the Ni54Mn25Ga17.5Ta0.5 alloy at room temperature. This is no changed martensite structure with non-modulated T martensite. In addition, the martensitic transition temperature obviously decreases from 350 °C to 208 °Cand hysteresis loop increases about 20 °Cwhen Ta substituted of Ni. The shape memory effect increased with the increase of pre-deformation, nevertheless, the shape recovery ratio appeared firstly increases and then decreases. When the pre-deformation is 10%, 15%, 20%, the shape memory effect of the alloy is 5.1%, 6.8% and 10%, respectively.