A new binary Mo-based cocatalyst consisting of partially reduced alpha-MoO3 (MoO3-x) nanoparticles and few-layer MoS2 nanosheets is deposited on AgIn5S8 nano-octahedrons (Octa-AIS) with only (111) facets exposed via an in situ growth process, in which the oxygen-deficient MoO3-x nanoparticles enable facile charge transport due to its high conductivity, while the few-layer MoS2 nanosheets provide more active sites and then excellent catalytic property for H-2 evolution. The resultant MoS2-MoO3-x hybrid cocatalyst utilizes the best properties of each component while mitigating their deficiencies, and thus realizes an effective enhancement of visible-light-driven H-2 evolution activity on Octa-AIS as compared with the single co-catalyst (such as MoS2, MoO3-x, and even Pt nanoparticles). This study not only presents a rare example of binary Mo-based cocatalyst consisting of MoS2 and MoO3-x components, but also paves a new way to develop an inexpensive photocatalytic system for energy conversion to achieve highly efficient H-2 evolution without noble metal-loading.