Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in (0-60% v/v) 1,4-dioxan (Dox)-water mixtures was studied pH metrically at 303±0.1 K and at an ionic strength of 0.16 M. The models contained ML, ML2, ML2H2, ML2H3 and ML2H4 species. The trend in the variation of stability constants with Dox content was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of Dox-water media was also presented.