In this study, austenite-martensite phase transformations which are formed by cooling effect in Fe-30% Ni-0-2% Mn alloy are investigated with Mössbauer spectroscopy and scanning electron microscopy. The single peak of the paramagnetic phase and the six peaks of the ferromagnetic phase of Fe-30% Ni-0.2% Mn alloy were observed in the Mössbauer spectrum. The internal magnetic field strength of ferromagnetic martensite phase was determined as 33.8 T and the isomer shift values were determined as - 0.11 mm.sec-1 and - 0.06 mm.sec-1, respectively, for the austenite and martensite phases. In this alloy, athermal transformation was observed. The results obtained are in agreement with literature.