The formation constants of binary complexes of Ca(II), Mg(II) and Zn(II) with glycylglycine in (0.0-2.5% v/v) TX100-water mixture were determined pH metrically at 303.0 K and an ionic strength of 0.16 mol L-1. The existence of various binary complexes was established from modeling studies using the computer program MINIQUAD75. The best fit chemical models were arrived at based on the statistical parameters like crystallographic R factor and sum of squares of residuals in mass-balance equations. The trend in the variation of stabilities of binary complexes with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. The distribution diagrams of the complex species are also presented.