The interactions of Cu(II), Cr(II) and Ni(II) metal ions with 1(2'-hydroxy-5'-bromophenyl)-3(4'-aminophenyl)-1,3- propanedione (L1) and 1(1'-hydroxy-5'-bromophenyl)-3(4'-nitrophenyl)-1,3-propanedione (L2) have been substituted at 0.1 M ionic strength in 70 % Dioxane-water mixture by Bjerrum method as adopted by Calvin and Wilson. It is observed that Cu(II), Cr(II) and Ni(II) metal ions from 1:1 and 1:2 complexes with ligands (L1 & L2). The data obtained were used to estimate and compare the values of proton-ligand stability constant (pK) and metalligand stability constants (log k). From estimated data (pK and log k), the effects of substituents were studied.