The nanocrystalline NiCr (x) Fe3-x O-4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been synthesized by microwave-assisted combustion method, and the effect of Cr3+ substitution on the structural and magnetic properties of NiFe2O4 was studied. Phase formation was identified by X-ray powder diffraction (XRD), which confirmed the formation of a cubic spinel structure for all the compositions. The lattice "a" of all samples decreases with the increase in Cr contents in the compositions. The elemental analysis by scanning electron microscopy-energy dispersive X-ray was in close agreement with the expected composition from the stoichiometry of the starting composition used for the synthesis. NiFe2O4 and NiCr0.2Fe1.8O4 nanoparticles (NPs) show features of superparamagnetin NPs, namely reduced and unsaturated magnetization together with the absence of coercivity.