MnZn ferrite nanoparticles (NPs) with MnxZn1-xFe2O4 ( x=0 and 0.6) compositions have been synthesized by sol-gel process. As prepared (AP) particles were annealed at 1200 °C in air to compare the physical properties of NPs with their bulk counterparts. The crystallite sizes of AP samples were estimated to be 18 nm for x=0 and 11 nm for x=0.6. The cationic disorder was evaluated from the Rietveld analysis of X-ray diffraction (XRD) data, which decreases with increasing annealing temperature. The average particle size of the AP samples is observed to be below 20 nm and transform into single-phase spinel structure of ∼ 500 nm long cylindrical rods of 60 nm-diameter for x=0.6 , when annealed at 1200 °C in air. The magnetic properties of AP NPs show ferrimagnetic behavior below the blocking temperature ( T) and superparamagnetic behavior above the T. The observed magnetic characteristics corroborate well with the structural parameters obtained from the Rietveld analysis of the XRD data. © 1965-2012 IEEE.