The solution studies the proton-ligand stability constant pK and metal-ligand stability constants logk of binary (1 : 1) complexes of Ni(II), Cu(II) and Zn(II) with substituted thiopyrimidine drugs have been studied at 0.1M ionic strength in 70 % DMF-water mixture by Bjerrum method as adopted by Calvin and Wilson. It is observed that Ni(II), Cu(II) and Zn(II) metal ions form 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 metal-ligand stability constants (logk). From estimated data (pK and logk), the effects of substituents were studied.