Non-electrolyte complexes of the general formula [Co(Hdmg)2(HA)X] where Hdmg = dimethylglyoximato monoanion, HA = alanine, threonine or histidine and X = CI, Br, I, SCN were synthesized and characterized by elemental analyses, IR, UV-Visible and 1H NMR spectra. The complexes are pseudo-octahedral with two dimethylglyoximato ligands N-bonded to the metal in the equatorial plane, the two axial sites being occupied by one amino acid molecule and one halogen or pseudo halogen anion. The thermal behaviour of these cobalt(III) complexes, determined by thermogravimetry (TG) and differential thermal analysis (DTA), shows that the dimethylglyoximato ligand is thermally more stable than the two other ligands.