Abstract: The analytical function of temperature response on rear face is derived forpulse thermal diffusivity measurement using a trapezoidal energetic pulse. In ac-cordance with this, the expression for characteristic time of thermal diffusion isfound. It is concluded that Non-instantaneous Pulse effect originates from theduration of energetic pulse and the geometry factor related to its shape. Throughthe measuring and correcting of thermal diffusivity for thinner specimens, the cor-rection procedure is demonstrated.