The ferromagnetic resonance of single crystals of CdCr2S4and CdCrSe4has been investigated as a function of temperature at 9.49 and 24.24 GHz. The CdCr2S4crystals were grown by vapor transport, and the CdCr2Se4crystals were grown from CdCl2flux. The magnetocrystalline anisotropy and linewidth were found to be dependent on sample. TheK1at 4.4°K varied between 3.8×103and 4.4×104erg/cm3for CdCr2S4and 2.2×103and 1.8×104erg/cm3for CdCr2Se4. These values are in good agreement with those based on a calculation using the single‐ion model of anisotropy. The linewidth of the more anisotropic samples was found to be orientation‐dependent and broad compared to the less anisotropic samples. The narrowest linewidth observed at 4.4°K was 37 Oe. This value is higher than expected for these materials and may be caused by crystalline imperfections. It is suggested that the observed variation of properties with sample may be due to small concentrations of divalent chromium.