Ni(II), Cu(II), Ag(I) and Hg(II) form 1:2 (metal-ligand) complexes with 4’-morpholinoacetophenone thiosemicarbazone. The stability constants of these complexes in 60% (v/v) aqueous DMF were determined at different ionic strengths (0.07, 0.13 and 0.20 M) and at different temperatures (25, 30, 35 and 40 +/- 0.1-degrees-C) using a spectrophotometric method. From these constants, the thermodynamic stability constants and thermodynamic parameters (DELTAG(formal), DELTAH(formal), DELTAS(formal)) were calculated.