The acid dissociation constant of the two ligands 3-thioacetyl-3-amino-1.4-naphthoquinone [L1] and 2-benzoyl-3-amino-1.4-naphthoquinone [L2] in ethanolic solution was determined by pH-metric technique at different temperatures (25, 35°C), and at various ionic strengths (I= 0.02, 0.1, 0.15 M NaCl) The stability constants of the formed chelates between L1 and L2 and Co(II) , Ni(II) and Cu(II) at two temperature degrees (25, 35°C) have been investigated . It has been found that it increase in the order Co (II) < Ni (II) < Cu (II) .The thermodynamic parameters (ΔGo, ΔHo, ΔSo ) of the chelates were deduced.