Abstract: In this paper we report the studies on polarization fatigue in ferroelectric vinylidene fluoride and trifluoroethylene copolymer films.It is found that,with the increasing number of polarization switching,the voltage corresponding to ferroelectric switching peak gradually shifts towards higher voltage,the shape of polarization-voltage hysteresis loops is strongly modified and becomes rounded,and the remanent polarization is also gradually decreased.Furthermore,experimental results indicate that only bipolar electrical stressing can cause ferroelectric fatigue and the fatigue rate is frequency dependent: the lower the frequency,the higher the fatigue rate.The origin of ferroelectric fatigue in ferroelectric polymers is discussed.