The potential importance of built‐up films of barium stearate for making dielectric devices has led to the necessity of the study of their ac breakdown characteristics. In the present work, the thickness and frequency dependence of the ac breakdown field has been reported in the thickness range 100–1500 Å and in the frequency region 10–200 kHz. The breakdown field is found to vary with thickness asd–a(&agr;=0.68) and the breakdown voltage is found to increase with increasing thickness and frequency in the specified ranges. Although the experimental results could not be interpreted at present, the results obtained may prove useful in ac device applications of the films.