The thermal behaviour of the compound K-2[Ni(C2O4)(2)(H2O)(2)].4H(2)O has been studied by thermogravimetry and differential thermal analysis. Experiments were carried out in dynamic atmospheres of argon-oxygen and argon, respectively,over the temperature range 20-600 degrees C. Thermoanalytical data show that the surrounding atmosphere significantly influences the dehydration process as well as the final products. In the oxidative atmosphere, the six water molecules are released during two almost overlapping endothermic steps, whereas in the inert atmosphere, the free water molecules and the coordinated ones are lost in separate stages. In both cases, dipotassium carbonate has been found as the final product, together with NiO in the oxidative environment and metallic nickel in the inert atmosphere.