The stability constant values of ternary complexation by transition metal ions such as Co (II), Ni(II),Cu(II),Zn(II) with allopurinol and ascorbic acid has been evaluated by potentiometric method. The ionic strength was maintained by NaNO3 A computer based SCOG program is used to calculate stability constants. The trend in the stability constants varies for ternary complexes Co(II) > Zn (II) > Cu (II) > Ni(II).