Activity of a cadmium sulfide photocatalyst, for hydrogen production by decomposition of water using visible light, depends on the protocol used for its preparation. In the present work, unsupported and alumina-supported CdS photocatalysts were prepared by various techniques and characterized by N-2 adsorption, X-ray diffraction, electron diffraction, and X-ray photoelectron spectroscopy. The results indicate that the activity is strongly affected by the dispersion and distribution of CdS on alumina. High dispersion and preferential distribution of CdS on the surface of alumina yield superior activity. The catalyst activity has been explained with the help of its microstructure.