Magnetic nanoparticles of Co0.5Mn0.5Fe2O4 have been synthesized using sol-gel combustion method in which citric acid was used as the complexing agent. The structural, thermal and magnetic properties of synthesized powder particles have been studied as a function of calcination temperature. It is observed that the coercivity attains maximum around the particle size of 32 nm. The presence of functional group was identified by Fourier transform infrared (FTIR) spectroscopic studies. The saturation magnetisation values increase with the size of the particles and then coercivity of the nanoparticles varies significantly as calcination temperature increases. © 2008 Elsevier B.V. All rights reserved.