An additive, silver nitrate (AgNO3), was used to prepare nanostructured films of cadmium sulfide (CdS) via a metallorganic chemical vapor deposition (MOCVD) process by using a single source precursor of CdS. The silver (Ag) vapors or clusters resulting from the thermal decomposition of the additive served as the extra active sites for nucleation of both surface and gas-phase growth of CdS and had an apparent influence on the morphology and photoluminescent (PL) property of the resulting CdS deposits. When the additive was present, a reduction in characteristic size of the CdS deposit structure was observed. In the first half of the reactor, an apparent morphology change and a significant increase in the deposition rate of CdS deposits were observed, attributable to the increased nucleation rate. In the second half of the reactor, both deposit morphology and eposition rate did not change much, possibly due to the depletion of Ag vapors or clusters. The PL quantum yield of the deposit was much enhanced in the additive case. In addition, the gas-phase formed particles became more numerous and much finer in size due to the increased nucleation rate. The nanoparticles collected at the reactor exit were smaller than 5 nm, giving rise to a substantial blue-shift in ultraviolet/visible (UV/Vis) absorption (from 500 to 375 nm) and corresponding photoluminescence (from 520 to 430 nm) spectra because of the strong quantum confinement effect.