Electrolytic conductivities of some alkali metal halides, MX (M+ = Li+, Na+, and K+; X- = Cl-, Br-, and I-), NaBPh4 and Bu4NBr have been investigated in (20, 40, and 60) mass% (dimethyl sulfoxide (DMSO) in DMSO + acetonitrile) at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance Lambda degrees the association constant K-A and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu4NBPh4 as the "reference electrolyte". The association constant K-A tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter Delta G degrees and Walden product Lambda degrees eta. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents. (C) 2009 Published by Elsevier Ltd.