The ferromagnetic resonance (FMR) line shapes of Gd-substituted calcium vanadium garnets Y1.6−zCa1.4GdzFe4V0.4Zr0.6O12(0.8⩽z⩽1.4) have been studied as the function of the Gd content. The samples had been synthesized by two different routes, with porosities varying from 0.23&percent; to 8.9&percent;. The FMR linewidth,&Dgr;H, in low porosity samples is small (15–20 Oe) and becomes seven to eight times higher in high porosity samples. The linewidth can be explained on the basis of Schloemann’s theory of anisotropy and porosity broadening in polycrystalline materials. The line shape is Lorentzian for low porosity and Gaussian for high porosity samples. This variation of the FMR line shape with porosity is explained on the basis of the stochastic theory. ©1997 American Institute of Physics.