Chemistry Department. Vidya Bharti Science College, Vidya Bharti Mahavidyalaya, Karanja (Lad), Akola-444 105 Government V. M. V. Amravati Manuscript received 16 November 1993. revised 11 April 1994. accepted 17 June 1994 The interaction of CoII, Nill and Cull with 2'-hydroxy-5'-methyl-3-nitrochalcone (1), 2'-hydroxy-3'-nitro-5'- methyl-3-nitrochalcone (2), 3-(2-hydroxy-5-methylphenyl)-5-(3-nitrophenyl)isoxazoline (3) and 3-(2-hydroxy­3-niro-5-methylpheny1)-5-(3-nitrophenyl)isoxazoline (4) have been investigated potentiometrically in 70% dioxane-water mixture at 0.1 M ionic strength. The metal ions form 1 : 1 and 1 : 2 complexes with all the ligands. Proton-ligand and metal-ligand stability constants have been determined by Irving-Rossotti's expression. Spectrophotometric investigation of the Cull complexes with substituted chalcone and isoxazoline has shown 1 : 1 and 1 : 2 complex formation. The spectrophotometric method is compared with potentiometric method. The results obtained of stability constants are in good agreement.