Formation of complexes of transition metals like Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with ligand N-[2-hydroxy- 1-naphthalidine]-2-chloroaniline was studied by the potentiometric technique at 27 ± 0.10C in 60% (v/v) dioxane – water medium at 0.1M (NaClO4) ionic strength were determined by Calvin Bjerrum method as modified by Irving & Rossotti.