The aim of this research was to develop strong polyvinylidene fluoride (PVDF) piezoelectric films. The piezoelectric activities were investigated by measurement of d₃₁ coefficient. In this work , piezoelectric films were prepared by stretching PVDF films. After annealing, aluminum was evaporated to both sides of the films to form electrodes. After poling by high electric field piezoelectric films were obtained. In measuring d₃₁ , stress was applied along the stretched direction of the films and charge transferred between electrodes was measured. It was found that d₃₁ of prepared films increase with poling time (tp) , poling temperature (Tp) and poling electric filed (EP) , but decrease with stretched radio (1/10) . The optimum condition for the preparation of high piezoelectric films is : Tp ≤ 80 ℃ , Ep ≥ 80 MV/m, tp ≈ 20 minutes and 1/10 = 4. The piezoelectric PVDF films obtained in this work can be used as acoustic transducers for various acoustic instruments.