Measurements of the thermopower were carried out, from room temperature down to 10K, on the colossal magnetoresistance (CMR) thin films of the Pr2/3Sr1/3MnO3(PSMO) sample, which showed a dramatic reduction in the 1/f noise spectrum reported previously. At low temperatures, the thermopower is negative and shows metallic diffusion behavior of linear temperature dependence. As the temperature goes up near 150K, the thermopower reduces dramatically to show the behavior of 1/T temperature dependence,which is consistent with the prediction of the small polaron model for the high temperature phase of CMR materials. Compared with the temperature dependence of the resistance and the property of the 1/f noise near the phase transition peak, the conclusion can be reached that the percolation-typed phase separation exists in the phase transition temperature region.