Chemical speciation of L-Asparagine complexes of Pb(II) and Cd(II) in presence of (0-50% v/v) dimethyl sulfoxide(DMSO)-water mixtures has been studied potentiometrically at 303.0 K and at an ionic strength of 0.16 mol L-1. The models containing different number of species were refined by using the computer program MINIQUAD75. The number of species in the models is chosen based on exhaustive modeling. The predominant species formed are of the type ML2, ML2H, and ML2H2. The best fit chemical models were chosen based on statistical parameters. The convenience of the models is ascertained by studying the effect of errors in concentrations of ingredients. The trend in variation of stability constants with change in the composition of medium is explained on the basis of predominant electrostatic and non-electrostatic forces. Chemical speciation was discussed based on the distribution diagrams. DOI: http://dx.doi.org/10.4314/bcse.v30i1.6