A method and apparatus are described which enable a sensitive, reproducible measure of the saturation magnetostriction &lgr;sof thin ferromagnetic films. The use of low frequency magnetic resonance probes simplifies the measurement of the changes in the film anisotropy field which occur due to strain in a magnetostrictive film. The applicable equations for the technique are presented with the result that &lgr;sis shown to be directly proportional to an easily measured current and inversely proportional to the deflection of the substrate center. Successful measurements have been performed on films as thin as 100 Å and as thick as 2000 Å. Conducting substrates are permissible.