We have investigated structural and magnetic properties of epitaxial (100) Ni80Fe20 films grown on relaxed Cu/Si(100) seed layers. The crystallographic texture and orientation of these films was analyzed in situ by reflection high energy electron diffraction (RHEED), and ex situ by x‐ray diffraction and cross‐sectional transmission electron microscopy (XTEM). In particular, RHEED intensities were recorded during epitaxial growth, and intensity profiles across Bragg rods were used to calculate the surface lattice constant, and hence the film strain. XTEM analysis indicated that the epitaxial films had atomically abrupt interfaces. The magnetic properties of these epitaxial films were measured in situ using magneto‐optic Kerr effect magnetometry. Large Hc (10–20 Oe) was observed for epitaxial Ni80Fe20 (100) films less than 10.0 nm thick whereas for larger thicknesses, Hc decreased to a few Oe with the appearance of a uniaxial anisotropy. Correlations were made between magnetic properties of these epitaxial films and the strain in the film.