Abstract Molecular magnet nickel(II) hexacyanoferrate(III) powder Ni 3[Fe(CN) 6] 2·XH 2O was prepared by coprecipitation method. The coprecipitated powder was annealed in vacuum at different temperatures of 140, and 160 °C. Water molecules contained in Prussian blue analogues were removed by heating. The annealing of Ni II ferricyanide induced an inner charge transfer from Ni II towards Fe III to form the mixed valence system Ni(II) Ni(III) ferri-ferro-cyanide. Variation of magnetic properties with different annealed temperatures was studied by elemental analysis, powder X-ray diffraction, transmission electron microscopy, Fourier transform infrared, and Mössbauer and magnetization measurements. The differences in magnetic phase transition temperature, coercivity, remanence and effective magnetization are studied. Differences in magnetic properties may be attributed to a partial charge transfer from Ni II to Fe III.