Strain sensitivity of amorphous ͑Fe 90 Co 10 ͒ 78 Si 12 B 10 sputtered film was studied in detail, so as to examine the potential of film for highly sensitive microstrain gauges. The film exhibited the figure of merit Fϭ(⌬/)/⑀ ͑change in film permeability per unit strain ⑀͒ of 1.2ϫ10 5 , the value of which is comparable to that of amorphous ribbons. Reflecting the large value of F, the high-frequency impedance of the film was also subjected to change due to strain: the change in impedance of 46% was observed at 100 MHz applying a strain of 300ϫ10 Ϫ6 . It is also demonstrated that utilizing the strain-dependent impedance, a small strain of 0.2ϫ10 Ϫ6 can be detected with the film.