1(O-Arsonophenylazo)-2- naphthol - 3,6 - disulphonic acid (APANS, H5A), an excellent agent due to presence of five electron donating functional groups, have been found to form complexes with various metal ions. It is used in determining the composition and the stability constants of a number of complexes formed under a limited pH range using spectrophotometric methods. In the present investigation. a detailed study on the chelation reactions of APANS and pair of ligands, APANS-en and APANS-mpn with transition metal ion, fe2 has been carried out at 200 (r=0.10m KNO3/Na2SO4) employing the pH - metric method. From the experimental data pH Vs volume of alkali crrves were plotted and were utilized to calculate moles of alkali used per mole of ligand (d). Further, pH vs d, curves were platted and analysed.