Abstract: The dependence of the saturation magnetic moment, ferromagnetic resonance (FMR) and Mössbauer effect on the composition and temperature for the Y_3-xGd_xFe₅O₁₂ single crystal system with x=0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 have been studied at a wide range of temperature. The variations of thermo-magnetic curves and compansation points with composition are explained by the theory of ferrimagnetism. The theoretically calculated results agree well with those of experiments. The line-widths of FMR for several theories are evaluated. It is found that the experimental results can be well explained by the phenome-nological theory of ferrimagnetic resonance with some reasonable assumptions. It is also tcund that the substitution of Gd³⁺ for Y³⁺ ions in the dodecahedral site has hardly any significant influence on the Mössbouer parameters of Fe³⁺ ions in the tetrahedral and octahedral sites, whose spectra can be resolved into two subspectra again.