Investigation of the thermal decomposition of [Co(NH3)(6)](2)(C2O4)(3). 4H(2)O has been carried out in air and argon atmospheres under non-isothermal, isothermal and quasi-isothermal-isobaric conditions. Identification of intermediates and final products was carried out using spectroscopy (Far-IR, IR, UV-VIS), magnetic susceptibility and X-ray diffraction. The dissociation of the compound under investigation was found to occur in three stages in both atmospheres. The solid products formed at each particular stages of the decomposition has been identified.