The microstructure and magnetic properties of polycrystalline Fe100-xNix films have been studied by X-ray diffraction (XRD) and magnetic moment measurements. In the XRD pattern of Fe-Ni films, the values of area ratio, A(1 1 1)/A(2 0 0) for the XRD peaks, in the thickness dependence decrease rapidly with increasing film thickness in the films with a bias field applied parallel to the plane in order to introduce uniaxial anisotropy, but the values for the films without the field are nearly constant. The coercivity vs. thickness analyzed by using Neel's formula show that the values for the films with the bias field follow Neel's formula within the thickness range of 40-100 nm, except the range of 10-40 nm. This result indicates that there is a change in domain wall type at the thickness of 40 nm. From the results of thickness and temperature dependence of magnetization analyzed by using some theoretical models, the values of interaction strength between magnetic ions were determined. The electrical resistivity of films is found to be consistent with the Mayadas-Shatzkes model. (C) 2003 Elsevier B.V. All rights reserved.