Twelve new complexes NH4[Co(DH)2(SO3)(amine)]·t H2O (DH2=dimethylglyoxime) have been synthesized and characterized. Their i.r. spectra show the SO3 to be co-ordinated to the Co atom through the S atom. The thermal decompositions of a series of derivatives of this type have been investigated with a derivatograph. The first process is an endothermic dehydration reaction, occurring in a single stage or in two successive ones. The loss of the crystallization water is followed by another endothermic reaction, without a clear stoichiometry, which is referred to as “deamination”. At higher temperatures, exothermic pyrolysis processes occur. From the TG curves, kinetic parameters have been derived for the dehydration and deamination reactions.