Colloidal CdS and CdZnS nanocrystals (NCs) with massive S2--adsorption were synthesized via a one-step synthetic method. In the absence of a cocatalyst, the as-obtained colloidal CdS-NC photocatalyst achieves a superb H2-evolution rate of 6.86 mmol h-1 g-1 and an apparent quantum efficiency of 52.8% under visible light.