An apparatus for measuring thermal diffusivity includes a Raman spectroscope, a heating device, and a signal analyzing unit. The Raman spectroscope is utilized to measure a Raman scattering intensity of different sites of a film to be measured. The heating device is utilized to provide a controllable thermal driving wave. The signal analyzing unit is utilized to analyze the Raman scattering intensity from the Raman spectroscope and the thermal driving wave so as to evaluate the thermal diffusivity of the film to be measured.