The effect of thermal cycling on the characteristics of martensitic transformation was studied in Fe-17%Mn alloy. The thermal cyclic treatment was carried out with three types; room temperature ↔ 255℃, 300℃and 345℃ As the number of the thermal cycle was increased, the hardness was rapidly increased up to 5 cycles, and then was gradually increased with further cycle. The volume fraction of the εmartensite was also increased with increasing the thermal cycle. The dislocation density in the austenite was increased with increasing the thermal cycle, which resulted in a decrese in the Ms temperature by the strengthening of the austenite, In the zero-cycled specimen, the martensite volume fraction was burstly increased at and below Ms temperature, and was gradually increased with further cooling below about 100℃. On the other hand, in the 15-cycled specimen, the martensite volume fraction was slowly increased in the early stage, but rapidly increased in the range of 100℃ to 60℃. On further cooling, the volume fraction was gradually increased.