Molybdenum disulfide (MoS 2 ) is heralded as an exemplary two-dimensional (2D) functional material, largely attributed to its distinctive layered structure. Upon forming heterojunctions with reducing species, MoS 2 displays remarkable photocatalytic properties. In this research, we fabricated a novel heterojunction photocatalyst, FeS/MoS 2 -0.05, through the integration of FeS with hollow MoS 2 . This composite aims at the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)). A comprehensive array of characterization techniques unveiled that MoS 2 flakes, dispersed on FeS, provide numerous active sites for photocatalysis at the heterojunction interface. The inclusion of FeS seemingly promotes the formation of sulfur vacancies on MoS 2 . Consequently, this heterojunction catalyst exhibits photocatalytic activity surpassing pristine MoS 2 by a factor of 3.77. The augmented activity of the FeS/MoS 2 -0.05 catalyst is attributed chiefly to an internal electric field at the interface. This field enhances the facilitation of charge transfer and separation significantly. Density functional theory (DFT) calculations, coupled with experimental analyses, corroborate this observation. Additionally, DFT calculations indicate that sulfur vacancies act as pivotal sites for Cr(VI) adsorption. Significantly, the adsorption energy of Cr(VI) species shows enhanced favorability under acidic conditions. Our results suggest that the FeS/MoS 2 -0.05 heterojunction photocatalyst presents substantial potential for the remediation of Cr(VI)-contaminated wastewater.