Co1.5Fe1.5O4 ferrite with nano-sized grains has been prepared by chemical reaction of metal nitrates at different pH values. XRD pattern has shown cubic spinel structure. The samples prepared at pH similar to 11-12 showed ferromagnetism at room temperature, whereas the sample prepared at pH similar to 9.5 has shown superparamagnetic feature. Samples have shown large electrical conductivity (10(-2)-10(-4) S/cm), giant dielectric constant (10(4)-10(7)), and low dielectric loss (0.4-9). Magnetic and dielectric properties are strongly affected by the interfacial structure of nano-sized grains. To crosscheck the interfacial effects, magnetic properties of Co1.5Fe1.5O4 ferrite have been compared to that of a nano-composite, consisting of Co1.5Fe1.5O4 and non-magnetic NaNO3 particles. Cole-Cole plots of the complex dielectric spectra showed better insights of the interfacial effect in the samples. (C) 2013 Elsevier Ltd. All rights reserved.