The magnetization-induced uniaxial anisotropy has been investigated in zero-magnetostrictive Permalloy films by isothermal annealing. The samples, evaporated and successively stabilized in a rotating magnetic field, are annealed in a dc magnetic field without breaking the vacuum after deposition. The annealing behavior of the developed anisotropy field H_k is found to consist mainly of two definitely separated stages; the one (the first stage) is observed at a low annealing temperature, 100°_??_200°C, while the other (the second stage) at a higher anneal-ing temperature, above 300°C. The present report is concerned only with the first stage. The analysis of the annealing process indicates that the activation energy has a continuous distribution ranging from 0.7 to 1.0 eV with a frequency factor of about 10⁷sec^-1. It is noted that neither of the two quantities are dependent to any extent on the stabilization treatment, but are highly responsible for the saturation value of the first stage Hkh. Here H_k1∞ decreases with increasing stabilization temperature and its time. A model to explain consistently these annealing features is also proposed.