Pure and strontium doped zinc ferrite (Zn1-xSr xFe2O4) nanoparticles were prepared by the microwave combustion method using urea as the fuel. Rietveld refinements of X-ray diffraction pattern confirm the formation of single cubic spinel phase with an average crystallite size in the range of 25-42 nm. The broad visible emission band is observed in the entire photoluminescence spectrum. The estimated band gap energy is found to decrease with increasing Sr content, i.e. 2.1-1.72 eV. Magnetic measurements at room temperature revealed that at lower Sr concentration (x≤0.2), the system shows a superparamagnetic behavior, whereas at higher Sr concentration (x≥0.2), it becomes ferromagnetic. The relatively high saturation magnetization of the as-prepared Sr-doped ZnFe 2O4 nanoparticles suggest that this method is suitable for preparing high-quality nanocrystalline magnetic ferrites for practical applications. The mechanism for the formation of ZnFe2O4 by the microwave combustion method is also discussed in the present study. Microwave combustion produced sufficient energy for the formation of ZnFe 2O4, because of its homogeneous distribution within the raw materials. This results in the formation of nanoparticles and early phase formation within few minutes of time. © 2013 Elsevier Ltd and Techna Group S.r.l.