This paper describes the development of a quick and simple method which can be used to measure the thermal diffusivity of fine powders. The method is based on measuring and analysing the phase lag which evolves in a cylindrical sample of powder subjected to an oscillating temperature wave originating at its axis. The variation of this phase lag with frequency has been analysed using both an analytical solution and a finite difference model. The analytical solution is the quicker method but the finite difference method is considered to be the more accurate. There is, however good agreement in the values found from both solutions. These solutions were applied to the results obtained from tests on three powders and their apparent Thermal Diffusivities are close to those predicted using other methods. As a comparison a test was performed and analysed with the rig filled with paraffin wax and the value obtained is close to that published in the literature.