Vapour pressures were determined at 20degreesC for aqueous 2-iso-butoxyethanol (ME). Partial pressures and hence, the excess chemical potentials of iBE were calculated by the Boissonnas method. Excess partial molar enthalpies were measured, and the excess partial molar entropies of iBE were then calculated at 20degreesC. These data and their mole fraction dependence indicated that there are three mixing schemes operative, in the same way as in aqueous 2-n-butoxyethanol (nBE) studied extensively by us. The details of each mixing schemes are identical, but the locus of the transition between mixing schemes I and II occurs at a smaller mole fraction than for aqueous nBE. This suggests that iBE is a stronger hydrophobic solute than nBE, which is consistent with the common understanding.