Abstract The solid state thermolysis of a series of 24 organo(aquo)cobaloximes and 19 organo(pyridine)cobaloximes has been investigated by differential scanning calorimetry and thermogravimetric analysis. In the most favorable cases three distinct transitions are observed by both techniques which may be assigned to loss of the axial (aquo or pyridine) ligand, loss of the organic ligand, and decomposition of the ‘core’ bis(dimethylglyoximato)cobalt complex. The temperatures for the first transition for the aquo complexes correlate reasonably well with the Taft polar substituent constant, σ*. In addition, a number of highly significant correlations were found between the temperature of the first transition and rate constants for ligand exchange processes in solution.