In continuation of our previous work here also, we have been interested in studying the stability of complexes of transition metals with biologically active ligands. Here we are presenting determination of stability constant of complex compounds using ligands synthesised from 5-Methyl furan-2-carbaldehyde and 7-methoxy naphthalene-2 -amine with bivalent transition metals i.e. Co(II), Ni(II), Cu(II) and Zn(II). Schiff's base ligands were synthesized by the condensation reaction of 5-Methyl furan-2-carbaldehyde with 7-Methoxy naphthalene -2 -amine. Nitrate salts of divalent cobalt, nickel, copper and zinc were estimated by standard volumetric and gravimetric methods. Ligand was analysed for elements by reported methods. pH metric titrations were carried out in an inert atmosphere of nitrogen gas at constant ionic strength of 0.1M KNO 3 with the help of digital pH meter.Stability constant of complexes of these metals with the ligands synthesized were computed by Irving-Rossoti technique 1 modified by Calvin Bjerrum 2 at temperatures 298K. The stability constant values of metals for the given ligand at the given temperature were found to be in the order Cu (II) > Ni(II), Co(II) > Zn (II). This result is in agreement with the natural order proposed by Irving-William. . A large number of such chelates have been synthesized, their structure and activity have been studied, but little is known about its stability in solution which will be its functioning condition. INTRODUCTION ExperimentalNitrate salts of divalent Co, Ni, Cu and Zn all were E. Merck. All other chemicals used were Anal R grade and used without further purification. Elemental analysis of metal salts were done by volumetric and gravimetric methods 11. Double distilled and deionised water was used throu778ghout the experiment. All titrations were done in aqueous-dioxane medium in the ratio 3:2 (v/v). Dioxane was purified by standard method.Schiff's base ligands were synthesised by reported method 12 1.5 g of 3-Methyl furan-2-carbaldehyde in solution were mixed with 3.5 g 7 -Hydroxy naphthalene -2 -amine. The mixture was refluxed in the presence of glacial acetic acid for 3 hours. The solution was concentrated and cooled to 0 0 C. The product obtained was filtered, washed several times and recrystallised from ethanol. The yield of product was nearly 2.40 g Solution of metal salts, ligands, electrolytes etc were prepared in doubly distilled CO 2 free water. Strength of various solutions used were tabulated in Table - A R T I C L E I N F O A B S T R A C TIn continuation of our previous work here also, we have been interested in studying the stability of complexes of transition metals with biologically active ligands.Here we are presenting determination of stability constant of complex compounds using ligands synthesised from 5-Methyl furan-2-carbaldehyde and 7-methoxy naphthalene-2 -amine with bivalent transition metals i.e. Co(II), Ni(II), Cu(II) and Zn(II). Schiff's base ligands were synthesized by the condensation reaction of 5-Methyl furan-2-carbaldehyde ...