Ion solvation investigations in binary solvent mixtures are important from a fundamental and technological view point. Iso dielectric mixtures are important from the view point of ion solvent interactions as these are not affected by changes in dielectric constant of the solvent mixtures and hence the chemical effects of solvents on ion solvatiion can be better delineated such studies on the solvation behaviour of the metal cryptand complexes in isodielectric solvent mixtures have to be studied in detail and in this paper results of the study of ion solvation behaviour of AgI-cryptand 222 perchlorate in the isodielectric solvent mixtures of methanol + N methyl-2-pyrrolidinone (NMP) over the complete range of solvent mixtures at 303 K are reported and they are compared with those in other binary solvent mixtures and with the uncomplexed salt. © 1999 CECRI.