The structural properties and relaxation processes of magnetization in [Ni 81 Fe 19 (t 1 )/Ru(t 2 )] N superlattices (N=number of bilayers) were analyzed by ferromagnetic resonance (FMR) with a fixed microwave frequency. One series of samples was deposited with constant NiFe layer thickness (t 1 ) and variable Ru layer thickness (t 2 ); the other series, with constant t 2 and variable t 1 . A single FMR mode was observed for t 2 <15Å and t 1 >75Å and it has been attributed to the resonance of the exchange-coupled NiFe layers across the Ru interlayers. For the other values of t 1 and t 2 , several FMR modes appeared and they were associated to non-coupled magnetic phases with different effective magnetization formed during the multilayer growth. The FMR linewidths were analyzed as a function of the magnetic layer thickness and a strong dependence on t 1 −2 was observed. It was attributed to the contribution of the two-magnon scattering mechanism for the linewidth.