The dipole moments of thirteen aryl styryl sulphides and eleven aryl styryl sulphones have been determined. Among them are eightcis-trans isomeric pairs, four sulphides and four sulphones. The styryl group is found to conjugate with the sulphide function as an electron-withdrawing group. The angles which the styrylthio and styrylsulphonyl groups make with their axes of rotation are calculated. The observed dipole moments of the sulphides and sulphones are compared with the moments calculated by the vector addition of group moments. The dipole moments ofcis aryl styryl sulphides and sulphones are found to be generally lower than those of theirtrans isomers. An explanation is offered attributing the cause to sterically enhanced styryl-sulphur conjugation in thecis isomers.