The influence of ammonia concentration on stoichiometric, surface morphological, and optical properties of chemical bath deposited cadmium sulphide thin films has been studied systemically. Chemical bath deposition (CBD) of CdS thin films was carried out via using cadmium acetate as the cadmium ion source, thiourea as the sulphur source and ammonia as the complexing agent. Ammonia concentration was changed from 0 to 2.5 M. At ammonia concentration greater than or equal to 0.1 M and lower than 0.6 M, nanowires or flake-like structures were obtained. At ammonia concentration ranging from 0.8 to 2.0 M, uniform, dense, and continuously coated films were obtained. The energy dispersive X-ray spectroscopy (EDXS) analysis revealed that as the ammonia concentration changed from 0.1 to 2.0 M, the Cd/S ratio in the obtained film increased from 0.24 to 2.61. Not only typical cadmium-poor but also unusual sulphur deficiency phenomena were observed for CBD CdS thin films. The films deposited with ammonia concentration of 1.0 M show the highest degree of crystallinity and closest stoichiometry Cd/S ffi 1, and have a preferred orientation. The direct band energy gaps of as-grown films were found to be 2.23-2.77 eV. The formation mechanism of the films with various morphologies and cadmium and sulphur deficiencies are discussed.