Abstract: In this study, the results of experimental investigation carried out on Surface Potential Decay (SPD) after corona charge deposition for Polyethylene-Terephthalate (PET) material are presented. This work shows that the classical interpretation of potential decay in terms of injection or polarization is not sufficient. The experimental results have revealed that there is a cohabitation of two processes namely, polarisation and charge injection with respective parts (shares) changing according to initial potential value and temperature. This investigation has showed that the surface potential decay is highly conditioned by temperature, relative humidity and charge density initially layed down on the material. More over, humidity and temperature influence on SPD is not the same.