The improvement of adhesion in polypropylene(PP) films have been required from industrial applications. Generally, the presence of polar groups and the morphology of the PP film surface play a crucial role for gaining good adhesion. Corona discharge to the films is one of the techniques to change a surface, widely used for the production of electrets. In recent researches, a good piezoelelctric activity in polypropylene electret has been found in foams with thin walls. However, the polarization origin of PP electret with hetero- and homo-charges by corona discharge treatment is unclear.