Mesostructured wurtzite ZnS-nanowire-bundle/amine nanocomposites displaying remarkable quantum size effects are synthesized by using a mild-solution reaction using different amines, such as n-butylamine, ethylamine, and tetraethylenepentamine, Zn(NO3)(2)center dot 6H(2)O, and CS(NH2)(2) or Na2S center dot 9H(2)O as the precursors at temperatures ranging from room temperature to 180 degrees C. A possible mechanism for the shape-controlled growth of ZnS nanowires and nanocomposites is proposed. Increasing the reaction temperature or dispersing the composite in acetic acid or NaOH solution leads to the destruction of the periodic structure and the formation of individual wurtzite nanowires and their aggregates. The nanowire/amine composites and individual wurtzite nanowires both display obvious quantum size effects. Strong band-edge emission is observed for the wurtzite ZnS nanowires after removal of the amine. The optical properties of these nanocomposites and nanowires are strongly related to the preparation conditions and can be finely tuned. This technique provides a unique approach for fabricating highly oriented wurtzite ZnS semiconductor nanowires, and can potentially be extended to other semiconducting systems.