A new technique has been developed for measuring the thermal diffusivity of finite-length samples. The sample was in the form of a round rod surrounded by a cylindrical guard. Both the sample and the guard had a small heater attached to one end. The heater was turned on and the voltages of equally spaced thermocouples were plotted as a function of time. This procedure determined the boundary conditions necessary for the solution of the heat flow equation. The solution at the sample midpoint was obtained by assuming various values of thermal diffusivity. The value of thermal diffusivity which gave the best agreement between the computed solution at the sample midpoint and the experimental curve obtained at the midpoint was considered to be the best value for the thermal diffusivity. An IBM 650 computer was used to process the data.