In this research paper, we report synthesis of nanocrystalline ferrite materials with a general formula Ni0.5Zn0.5CrxFe2-xO4 (x=0.0, 0.3) by the surfactant (PEG) assisted hydrothermal method and a systematic investigation on the structural, compositional and magnetic properties of undoped and Cr3+ doped NiZn-ferrite nanoparticles. The structural, compositional and magnetic properties of prepared samples were investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometry (VSM). The XRD analysis of the synthesized samples confirmed the formation of single-phase cubic spinel structure and the average crystallite sizes of the nanoparticles were estimated using Debye-Schener's equation as 12.16 inn and 12.11 nm for undoped and Cr doped samples, respectively. The results of FT-IR analysis indicated that the functional groups of Ni-Zn spinel ferrite were formed during the hydrothermal synthesis process. Moreover, FE-SEM micrographs demonstrated that nanoparticles with narrow size distribution and without agglomeration were obtained. Magnetization measurements have shown that the particles have superparamagnetic behavior at high temperatures and ferrimagnetic behavior with relatively small coercive fields at low temperatures. The hysteresis curves of the samples exhibited the reduction of saturation magnetization and coercivity by Cr3+ ions substitution. Magnetization and the coercive field of the samples increase by decreasing the temperature. The blocking temperature TB is also decreased by Cr doping. The presence of superparamagnetism with very small coercivity (soft ferrite) indicating the samples are good candidates for applications in high-frequency transformers. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.