In recent years, BiOI has been extensively studied due to its excellent absorption ability of visible light. However, low energy conversion efficiency affects its potential for practical application. In this paper, MoS₂/BiOI composite was synthesized by two-step ways and applied to the photoelectrochemical (PEC)detection of hexavalent chromium (Cr (VI)). Through a series of optical characterization, the structure and morphology of the material were measured in detail. UV–Vis diffuse reflection spectra and photoluminescence (PL) further proved that MoS₂/BiOI have the excellent PEC properties. The PEC experiment proved that the prepared MoS2/BiOI has a wide linear range (0.05–160 lM) and low detection limit (0.01 lM, at S/N = 3), moreover, it has great application potential in actual samples