This paper presents the results of X-ray research on the structure of Cu/Ni multilayers magnetron-deposited on a Si (100) substrate. The multilayers, each consisting of a hundred Cu/Ni double-layers, but with a variable thickness of the Ni (1,2÷3nm) sublayer, were investigated. The thickness of the Cu sublayer was the same for all multilayers investigated and equalled 2nm. X-ray measurements were taken using filtered radiation with λCu=0.15405 nm and λCo=0.17902nm. The coatings were examined in respect of the angle at which the (111) reflection and satellite peaks appeared together. The obtained reflections were fitted using the Pseudo Voight curves. The thickness of the multilayer periods, resulting from the analysis of the diffraction pattern obtained for the above wavelengths of radiation, was compared. The thicknesses closest to those assumed in the deposition process were obtained for multilayers examined using radiation with Cu and utilizing the position of both satellite peaks, and multilayers examined using radiation with Co and utilizing the position of the main Cu/Ni(111) reflection and the S-1 satellite reflection.