In this paper, we will analyze the changes in the kinetics of the induced anisotropy due to preannealing in 300‐A˚ and 1‐&mgr;m‐thick Co94Zr6amorphous films. Samples were prepared by a dc sputtering method. A silicon wafer with SiO2overcoat was used as a substrate material, and a field of 200 Oe was applied during the deposition to induce uniaxial anisotropy. Based on x‐ray data and resistivity measurements, the films were considered amorphous. The samples were annealed in a magnetic field at temperatures up to 500 °C, and the annealing time was varied from 0.5 to 400 h. As previously reported, the anisotropy,Ku, in as‐deposited samples is a function of sample thickness and varied from 1.6×104ergs/cm3for 300‐A˚ film to ∼1×104ergs/cm3for 1‐&mgr;m films [T. Jagielinski, J. Appl. Phys.61, 3237 (1987)]. It was found that theKuin thick films is reversible, and the kinetics can be fully explained by the anelasticity model [T. Egami, Rep. Prog. Phys.47, 1601 (1984)]. The mean value of the activation energy is ∼2 eV for samples preanneled at 375 °C. However, in the case of thin films, an additional irreversible component of anisotropy, always along the direction of the field applied during the deposition, is observed. The magnitude is a growing function of annealing temperature, and is as large as 3×104ergs/cm3for a 300‐A˚ sample preanneled at 400 °C. The origin of the irreversible component of the anisotropy is not well understood. Based on x‐ray data, we concluded that this effect is not related to crystallization. However, since anisotropy is thickness dependent, the structure of the film‐substrate interface seems to be responsible for the irreversible part. The reversible parts of anisotoropy behave similarly in both thin and thick films and are 1.6×104ergs/cm3and 8×103ergs/cm3for 300‐A˚ and 1‐&mgr;m films, respectively.