Polycrystalline sample of Mn-3[Fe(CN)(6)](2)center dot xH(2)O was prepared by coprecipitation method. The coprecipitated powder was annealed in vacuum at different temperatures of 80, 100, 130, and 150 degrees C respectively. Changes of magnetic properties with different annealed temperatures were studied by Fourier-transform infrared, X-ray diffraction and magnetization measurements. The positive. value of the Curie-Weiss temperature indicates the existence of a predominant ferromagnetic interaction over the anti-ferromagnetic one in the compounds annealed at 80, 100, and 150 degrees C. The negative value of. in Mn-3[Fe(CN)(6)](2)center dot xH(2)O annealed at 130 degrees C appears to be the coexistence of a strong anti-ferromagnetic and a ferromagnetic interactions in the material. This is due to the existence of a relatively strong anti-ferromagnetic contribution between the neighbouring Mn atoms bridged by the oxygen atom of the water molecule. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim