Exploration of highly active and noble-metal-free photocatalysts for high-efficiency photocatalytic water splitting is of great importance. Herein, a facile and effective in-situ hydrothermal method has been developed for preparation of CdS/MoS2 heterostructures with a unique hollow microbox morphology for visible-light-driven water splitting into H-2. The influence of MoS2 is systematically investigated in terms of optical properties and photocatalytic activity of the CdS/MoS2 microboxes by varying the concentration of sodium molybdate. Under visible-light irradiation (lambda >= 420 nm), the CdS/MoS2 microboxes exhibit superior photocatalytic H-2 evolution activity (1.36 mmol/g/h) compared to pure CdS microboxes (0.04 mmol/g/h), corresponding to an apparent quantum yield of 14.5% at 420 nm. Photocatalytic mechanism study proves that the MoS2 nanosheets can serve as a co-catalyst and electron acceptor, for the effective promotion of electron transfer and separation of photogenerated charge carriers from CdS to further stimulate the surface H-2 evolution kinetics. Furthermore, the well-defined interior voids, low density and shell permeability of the hierarchical CdS/MoS2 microboxes also contribute to the improvement of the photocatalytic performance.