Abstract: By solving the lamb wave dispersion equation for NiTi sheet, the dispersion curves were drawn. Lamb modes more sensitive in detecting phase transformation of NiTi alloy were selected on the basis of the dispersion curves. PZT transducers were used to excite and receive S1 and S3 Lamb waves on NiTi sheet. The wave group speed was measured when temperature of NiTi sheet changed. The results showed that some marked changes were observed in the dependence of the group speed versus temperature during phase transformation and phase transformation temperature of NiTi sheet might be examined by the change of the group speed.