Without using any templates or surfactants, hierarchical ZnS-In2S3-CuS nanospheres with nanoporous structure are successfully synthesized via a simple and convenient process. The nanospheres are aggregations of densely packed nanoparticles and nanorods. Different to the oriented attachment (OA) mechanism reported in the literature, the formation of these nanorods is believed to follow a lateral OA mechanism (nanoparticles attach along the direction perpendicular to the crystallographic axes with lateral planes as the juncture) based on the experimental data. This process could be a general phenomenon and would provide a new insight into the OA mechanism. A detailed time-resolved TEM kinetic study of the formation of the complex structure is shown. The dipole mechanism and electric field-induced growth are found to be responsible for the final architecture. Photocatalytic activities for water splitting are investigated under visible-light irradiation (λ > 400 nm) and an especially high photocatalytic activity (apparent yield of 22.6% at 420 nm) is achieved by unloaded ZnIn0.25Cu0.02S1.395 prepared at 180 °C for 18 h because of their high crystallinity, large pore volume, and the presence of nanorods with special microstructures.