We developed a simple synthesis method for production of CoFe2O4 nanoparticles. The method is based on the solid state ball-milling and calcinations of acetate precursors and citric acid. The samples were characterized using X-ray diffraction, transmission electron microscope, Fourier transform infrared and energy-dispersive X-ray spectroscopy. Magnetic properties of the samples were studied using vibrating sample magnetometer and ac susceptibility measurements. The results show that the products mainly consist of CoFe2O4 nanoparticles. Magnetization measurements demonstrate the effect of calcination temperature on particle size and hence, on the magnetic properties of the CoFe2O4 nanoparticles. By increasing the particle size from 3.5 to 7.2 nm, the room temperature coercivity and magnetization increase from 0 to 152 Oe and from 8 to 30 emu/g respectively. Also, the low temperature calcinated samples. C250 and C30 are superparamagnetic in nature due to it's near-zero coercivity and remanence. We estimated the mean value of the effective anisotropy constant, K-eff=9.2x10(6) erg/cm(3). This value is much larger than the bulk value, due to the surface effects. (C) 2010 Elsevier B.V. All rights reserved.