Anionic polymerization technique has been utilized to synthesize a bilaterally sulfur-functionalized polystyrene, SCH3-polystyrene-SH. The synthesis scheme consists of (1) initiation of 4-vinylbenzylmethyl sulfide with sec-butyllithium to form a living sulfur-containing initiator, (2) polymerization of styrene, and (3) termination of growing polystyrene chain with ethylene sulfide. The resulting bilaterally sulfur-functionalized polystyrene is used to make polystyrene/gold nanoparticles (AuNPs) nanocomposite with AuNPs formed in situ in polymer solution through reduction of AuClO4. The effects of the polymer/Au molar ratio as well as the molecular weight of polymer on the size and dispersion of formed AuNPs have been studied, and the superiority of bilaterally functionalized polymer to unilaterally functionalized polymer has been demonstrated. The polystyrene/AuNPs composite has been characterized by GPC, H-1-NMR, C-13-NMR, EDS, TEM, UV-Vis, and DSC. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1268-1277