We present here the design of a novel and simple setup for measuring the thermal conductivity of thin films. This method is based on the well known principle of phase lag of a traveling thermal wave. In the present setup, the traveling thermal wave is generated in the thin film by irradiating its one edge by an infrared laser. The phase lag (&Dgr;&thgr;) between the excitation wave and the resulting thermal wave, at a variable distancedfrom the edge of the sample, is determined by measuring the deflection of another “probe-laser.” The thermal diffusivity is then directly calculated from the slope of the plot between &Dgr;&thgr; andd.This method offers an accuracy of better than ±5&percent;. ©1997 American Institute of Physics.