The design and performance of a magnetic susceptometer for thin films and surfaces is described. The device uses a 14‐MHz resonant circuit driven by a tunnel diode oscillator with a superconducting meander line as the inductive element. Magnetic properties of thin films deposited near the line in ultrahigh vacuum at low temperature affect the inductance of the meander line and thus the frequency. The device can detect a susceptibility change equal to that of a change in Fe thickness of 0.03 atomic layers. The minimum detectable change in the diamagnetism of superconducting Pb corresponds to a thickness difference of 10−3A˚. The effect of 10−6atomic layers of Fe can be detected by its depairing effect on a superconducting Pb film. The oscillator circuit including the film being studied is analyzed and the oscillation frequency calculated so that the effect of the various circuit elements can be determined. Suggestions for extending this technique are given.