A pyroelectric photothermal spectroscopy has been developed for evaluating optical absorption spectra of thin films. The temperature change in a film illuminated with chopped monochromatic light is measured with transparent temperature sensors consisting of pyroelectric materials, and the output voltage is employed to calculate absorption spectra. In a practical system, the absorption coefficient down to 102cm−1can be determined for thin films 1 &mgr;m thick at desired temperatures.