van der Waals (vdW) heterostructures have attracted immense interest recently due to their unusual properties and new phenomena. Atomically thin two-dimensional MoS₂ heterostructures are particularly exciting for novel photovoltaic applications, because monolayer MoS₂ has a band gap in the visible spectral range and exhibit extremely strong light–matter interactions. Herein, first-principles calculations based on density functional theory is used to investigate the effects of vdW interactions on changes in the electronic structure, charge transfer and photoactivity in three typical monolayer MoS₂/fullerene (C₆₀, C₂₆, and C₂₀) heterostructures. Compared to monolayer MoS₂, the band gap of the heterostructures is smaller, which can enhance the visible light absorption and photoinduced electrons transfer. The amount of charge transfer at interface induced by vdW interaction depends on the size of fullerenes. Most importantly, a type-II, staggered band alignment can be obtained in the MoS₂/C₂₀ heterostructure, leading to significantly reduced charge recombination and thus enhanced photocatalytic activity. These results reveal that fullerene modification would be an effective strategy to improve the photocatalytic performance of semiconductor photocatalysts.