Corrosion study was carried out with a non-stoichiometric polycrystalline Ni48.3Mn32.4Ga19.3 shape memory alloy. It has been demonstrated that in this alloy during cooling two martensite transitions take place while only one reverse transformation is observed. These were confirmed with dilatometric measurement and compression test. In the corrosion study, potentiostatic polarization measurement was implemented on the NiMnGa alloy at four temperatures. The temperatures are so chosen that specimens of different structures or with the same structure at different temperatures will be tested. The corrosion behavior of the alloy is interpreted by calculating the corrosion rates from the measured polarization curves. Immersion tests were also carried out to give further information about the corrosion properties of the alloy. From this study the corrosion behavior of the NiMnGa shape memory alloy in different structures has been demonstrated. The experimental results provide useful guidelines for further study toward the corrosion mechanisms and corrosion control of the NiMnGa alloys.