Ti30.5Ni49.5Zr10Hf10 alloy undergoes a B2 <----> B19' one stage martensitic transformation. Martensitic transformation temperatures decrease, but the hardness increases with increasing aging time, resulting from the effect of point defects/atoms rearrangement in B2 phase induced by aging at 450degreesC. Thermal cycling can also decrease the transformation temperatures while increasing the hardness of the alloy. The strengthening effects of aging and thermal cycling on the M-s (M*) temperature of this alloy follows the expression M-s = T-0 - KKDeltasigma y, in which K values are affected by different strengthening processes. Experimental results indicate that martensitic transformation temperatures of Ti30.5Ni49.5Zr10Hf10 alloy can be more effectively depressed by aging than by thermal cycling. The K value of this aged alloy is smaller than that of aged Ti40.5Ni49.5Zr10 alloy due to the former having the higher aged temperature and the less lattice distortion.