Polycrystalline CdTe thin films deposited by the Close Space Sublimation method (CSS) were characterized through measurements of thermoelectric power (alpha) and resistivity (rho) in order to determine the scattering mechanism which mainly affect their electrical transport properties. The results were interpreted with the help of theoretical calculations of alpha vs. T, carried out using a theoretical model developed specially for this purpose. This model includes scattering processes within the grains and at the grain boundaries. Some of the parameters used in the calculation of alpha were determined experimentally and the main approximations were justified from experimental measurements. The reliability of the model was tested by comparing the values of a calculated as a function of the temperature, with curves of alpha vs. T obtained experimentally in the range between 90 and 330 K. From these studies, it was found that the electrical transport can be attributed to transport of heavy holes induced by external fields (temperature difference in this case) and by phonon drag. At temperatures lower than 200 K, the effect of phonon drag predominates whereas, at temperatures greater than 200 K, the effect of the external field is significantly greater. It was additionally found that the electrical transport is mainly affected by the scattering of heavy holes with acoustic phonons and grain boundaries.