Deposition of CdS nanofilms was performed using the chemical bath deposition method, as a function of the concentration ratio of [S] to [Cd] (S/Cd) and of deposition temperature. As the S/Cd ratio and deposition temperature increased, the deposition rate of the films increased, and the transmittance was improved. With increasing S/Cd ratio, the crystallinity of the CdS nanofilms decreased due to the formation of small grains therein. Atomic force microscopy revealed that the surface morphology of the films became smooth with increasing S/Cd ratio and deposition temperature. The evolution of the grain formation showed that the slow deposition rate of the films leads to a small number of grains at the initial stage of the deposition, followed by fast grain growth, resulting in a rough surface. On the other hand, a fast deposition rate initially causes the formation of many grains on the entire surface as well as slow grain growth, making the films smooth. It is evident that the deposition rate affects the physical and optical properties of the films due to their different growth mechanisms.