The thermal diffusivities of engineering plastics had been studied by the revised photoacoustic piezoelectric (PAPE) technique. Firstly, the revised PAPE method was proposed and the corresponding experimental system was set up. The experimental system was calibrated and tested by investigating the diffusivity of pure aluminum and polytetrafluoroethylene(PTFE). The thermal diffusivities of eight kinds of engineering plastics were measured by the revised PAPE method. The results showed that engineering plastics have excellent insulation properties and the diffusivities are under 0.4 mm2/s. The theoretical and experimental results showed that the revised PAPE method can be used to accurately measure the thermal diffusivity of engineering plastics.