Department of Chemistry, University of Roorkee, Roorkee-247 667 Manuscript received 30 January 1984, accepted 10 August 1984 The thermodynamic stepwise stability constants, free energy, enthalpy and entropy changes for the formation of MnII, FeII, CoII, NiII and CuII ions with phthalanilic, 4-methylphthalanilic, 4-methoxyphthalanilic, 4-chlorophthalanilic, 4-bromophthalanilic and 4-nitrophthalanilic acids were determined. Analysis of the data indicated the chelation of phthalanilic acids through nitrogen of secondary amide and carboxylate groups.