Department of Chemistry, Nagpur University, Nagpur-440 010 Manuscript received 5 September 1984, revised 19 June 1985, accepted 29 October 1985 This paper reports potentiometric studies on some mixed ligand complexes of UVIO2 using nitrilotriacetic acid as primary ligand, and succinic, malic, maleic, fumaric, malonic, adipic, itaconic phthalic and mandelic acids as secondary ligands. The thermodynamic parameters, \(viz\) .∆G, ∆H and ∆S have been evaluated. The ∆G and ∆H values have been further separated into their electrostatic components ∆Ge, ∆He and cratic components ∆Gc and ∆Hc. Effects of change in dielectric constant and change in ionic strength have been studied on a few systems. The results are correlated on the basis of steric and structural characteristics of the chelates formed.