Two magnetic nanocomposites were prepared from nanocrystalline zinc oxide doped with different concentrations of iron oxide (5 and 10 wt. %). X-ray diffraction and scanning electron microscopy have shown the growth of ZnFe2O4 nanocrystallites with size below 10 nm within the ZnO matrix in a highly agglomerated structure. Ferromagnetic resonance (FMR) measurements have shown line arising from the ZnFe2O4 nanoparticles. Temperature dependence of the FMR spectra parameters (amplitude, resonance field, linewidth, integrated intensity) has been investigated in the 4–300 K range. Zero-field cooled and field-cooled dc magnetic magnetization study in the same temperature range allowed to determine the blocking temperature TB and compare the results of two applied magnetic methods. Temperature dependence of FMR integrated intensity curve displays a peak at TB ∼ 23 K while FMR amplitude curve peaks at TC ∼ 170 K, the Curie-Weiss temperature of the high temperature susceptibility.