Molybdenum sulfide serves as an effective nonprecious metal catalyst for hydrogen evolution, primarily active at edge sites with unsaturated molybdenum sites or terminal disulfides. To improve the activity at a low loading density, two molybdenum sulfide clusters, [Mo₃S₄]⁴⁺ and [Mo₃S₁₃]^2-, were investigated. The Mo₃S_x molecular catalysts were heterogenized on Sb₂Se₃ with a simple soaking treatment, resulting in a thin catalyst layer of only a few nanometers that gave up to 20 mA cm^-2 under one sun illumination. Both [Mo₃S₄]⁴⁺ and [Mo₃S₁₃]^2- exhibit catalytic activities on Sb₂Se₃, with [Mo₃S₁₃]^2- emerging as the superior catalyst, demonstrating enhanced photovoltage and an average faradaic efficiency of 100% for hydrogen evolution. This superiority is attributed to the effective loading and higher catalytic activity of [Mo₃S₁₃]^2- on the Sb₂Se₃ surface, validated by X-ray photoelectron and Raman spectroscopy.