A method for the rapid measurement of magnetic anisotropy is described. The instrument consists of a self‐exciting torsion pendulum containing the magnetic sample, which is suspended in a magnetic field in a furnace. The resonance frequency of the pendulum, which depends on the anisotropy energy in a known way, lies between 10 and 100 cps so that the time required for a measurement is shorter than in other methods. The instrument is therefore capable of following a rapidly changing anisotropy, e.g., during the magnetic annealing of the sample. The measurement of the anisotropy of a single crystal of Ticonal G magnet steel during cooling from 900° to 400°C in a magnetic field is described as an example.