The molecular structures of HX....SO 3 (X=F, Cl, Br) have been calculated by ab initio and density functional theory (DFT) methods. Calculations show that they are weakly bound van der Waals complexes rather than genuine electron donor-acceptor complexes since they have long intermolecular distances. At the MP2/6-311++G(3df,3pd) level, the intermolecular bond distances S....F, S....Cl, and S....Br are computed to be 2.667, 3.112, and 3.230 Å, respectively, while the angles H-F-S, H-Cl-S, and H-Br-S are computed to be 108.4 o , 87.4 o , and 85.6 o , respectively.