A technique for measuring internal friction in thin films (∼2000 Å thick) has been developed. The film is deposited onto a 1‐μ‐thick ribbon of fused quartz having a Q∼5000 and which is clamped at one end. The ribbon and film are set into clamped‐free flexural vibration (∼100 cps) and the vibration is monitored by means of a light beam and photocell. The measurement of the vibration decay constant is expedited by using a logarithmic amplifier. Film relaxation peaks with Q∼300 can be measured at temperatures up to several hundred °C. As an example of the use of the technique, the Snoek relaxation of C in bcc Fe has been measured in a 2500‐Å Fe film.