Microstructure and the correlated martensitic transformation behavior of melt spinning Ni₅₀Mn₂₉Ga_21−xTb_x (x = 0–1) ribbons have been studied by X-ray diffraction, transmission electron microscope and differential scanning calorimetry. Single phase of the orthorhombic martensite was monitored for x < 0.2 with the complete solid solution of Tb atoms. For x ≥ 0.2 dual-phase microstructure containing the martensite and hexagonal nanoprecipitates was formed. Geometric phase analysis (GPA) revealed that there was a local strain field in the matrix around the nanoprecipitates. The martensitic transformation was observed in all the ribbons. Besides the significant increasing of the transformation temperatures caused by the solid solution of Tb elements, the temperature span of martensitic transformation were expanded due to the hamper effect of nanoprecipitates, which is thought to be due to the energy barrier introduced by the nanoprecipitates.