This paper demonstrates the influence of the relaxation time of photoexcited charge species on the photoluminescence and photocatalytic activity for oxidation-reduction reactions by CdS nanostructures of different dimensions. CdS nanospheres (size similar to 10 nm) and different aspect ratio (17 and 23) CdS nanorods have been prepared by two different techniques. CdS nanorods formed by autoclaving is found to be more lengthy, wider (length similar to 170 nm and width similar to 10 nm) and having better crystallinity than CdS nanorods (length similar to 126 nm and width similar to 5.5 nm) prepared by refluxing under similar conditions. Characterizations have been done by optical absorption, fluorescence emission, time resolved fluorescence decay, scanning and transmission electron microscopy, X-ray diffraction and BET specific surface area measurements. Relaxation lifetime of photoexcited electron-hole pairs is measured to be 20, 24 and 116 mu s for CdS nanosphere, shorter and longer CdS nanorod, respectively, seems to be responsible for the observed fluctuation in photoluminescence and photocatalytic activity. The photooxidation rate of salicylic acid (0.5 mM) and photoreduction of p-nitrophenol (0.2 mM) are significantly improved with increasing dimensions of CdS nanorods despite having a comparable surface area (81 and 76 m(2) g(-1)) and CdS nanospheres (18 m(2) g(-1)) exhibit poor photocatalysis. The better delocalization of charge species along the radial as well as longitudinal dimensions of CdS nanorods, higher crystallinity and delayed recombination time facilitate electrons or holes for active participation in the photoinduced reactions, and Au deposition always displayed superior photoactivity. (C) 2013 Elsevier B.V. All rights reserved.