In the design of structures made of engineering plastics by analysis, the most important mechanical property is fatigue strength. In this paper, in order to obtain fatigue strength of engineering plastics namely PC, PBT and PEEK, the fatigue test applied cyclic out-of-plane bending is performed on three kinds of specimen which is hour glass shape, a center circled hour glass shape and a strip with a center circle hole. The fatigue tests were performed in the wide range of failure life from 5000 to 10^7 cycles. It is cleared by the test that (a) low cycle fatigue life of PC, PBT and PEEK is almost equal each other and (b) fatigue endurance limits of PBT and PEEK is equal each other, but their values is 2.8 times that of PC. These fatigue strength behaviors of engineering plastics is different from that of general metal materials
