CdS quantum dots deposited on carbon nitride (g-C3N4) nanosheets have been synthesized by ultra-low temperature (-60 °C) liquid phase precipitation reactions. The obtained CdS quantum dots were uniformly distributed on the surface of the g-C3N4 nanosheets with an average diameter of 5 nm. Correspondingly, CdS/g-C3N4 exhibits a highly enhanced photocatalytic performance.