Photocatalytic hydrogen production with semiconductor catalyst is one of the best techniques to produce green hydrogen gas. This research investigated the effect of sulfur content on phase transformation of bimetal zinc nickel oxide to oxysulfide, which simultaneously affected the performance on photocatalytic hydrogen production. Different amounts of sulfur precursor (0, 0.25, 0.5, 0.75 and 1 mmol) were added to the bimetal oxide during the hydrothermal synthesis. The as-prepared catalysts were carefully characterized with necessary analyses such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis spectrophotometer, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, Brunauer-Emmett-Teller (BET) and transient photo current analyses. The sulfur content significantly affected not only the morphology and phase structure but also greatly improved the hydrogen production rate. The maximum hydrogen production rate of 15,000 μmol/g.h was achieved by using S-0.75 catalyst, which was 333-fold as compared to that with the catalyst before phase transformation. Our design of ZnNiOS had an exceptionally high photocatalytic activity as compared to single-phase oxide and sulfide. Herein, we demonstrated an important insight and material design about the effects of sulfur content on phase transformation, catalyst morphology, and photocatalytic activity.