CdS nanorods were successfully synthesized by pyrolysis using trioctylphosphine (TOP) as a coordinating solvent. For this pyrolysis, cadmium acetate dihydrate and sulfur powder were used as the cadmium source and sulfur source, respectively. The structure, morphology, and optical properties of the prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) 31P spectroscopy. The effects of different molar ratios of Cd-to-S and the reaction concentrations on the morphology and size of the CdS nanostructures were investigated. The results indicated that the wurtzite CdS nanorods, with a typical diameter of 4.5 nm and a length of up to 28.0 nm, had a preferential [001] growth direction and displayed a quantum confinement effect. We also proposed a possible formation mechanismfor the CdS nanocrystals based on the experimental results.