Studies of Pb(II) with some amino acids (L-Serine and LThreonine) and Ascorbic acid have been carried out polarographically at pH =7.30±0.01, µ=1.0M KNO at 25°C.Pb(II) 3 formed 1:1:1, 1:1:2 and 1:2:1 complexes with L-Serine and LThreonine used as primary ligands and L- Ascorbic acid used as secondary ligand. The trend of stability constants of simple complexes was L-Serine > L-Threonine. The values of stability constants (log varied from 2.25 to 11.45 confirm that these L- amino acids or in combination with L-Ascorbic acid, their complexes could be used against Pb(II) toxicity. The stability constants of mixed ligand complexes have been evaluated by the method of Schaap and McMasters. For the comparison of the simple and mixed-ligands complexes, the mixing constants (K )m and stabilization constants (K ) have been measured The positive values of the mixing constants and stabilization constants show that the ternary complexes are more stable than the binary complexes.