Abstract: In order to get the quantitative relationship between the decay time constant(DTC)of the laser-induced thermoelectric voltage(LITV)signals and the physical parameters of the thin films,YBa2Cu3O7-x,La0.67Ca0.33 MnO3, La0.67Ca0.33 MnO3 thin films were prepared by means of pulsed laser deposition.The corresponding LITV signals were detected with these films illuminated by 248nm pulsed laser.An exact function of DTC was deduced based on the interaction between the laser pulses and the films.The measured LITV signals were observed decaying exponentially,which is in agreement with the model of LITV effect.The DTC is just limited by the thermal transition properties of the films,and is the function of the thermal diffusion constant.According to the measured decay time,the thermal diffusion constants of the thin films can be calculated.Thus the measurement of DTC of LITV signals is a new way to investigate the thermal diffusion constant of thin films.