<p>Understanding the sulfur isotope cycle is essential in developing genetic models of porphyry copper deposits. In this paper, we characterize the sulfur isotope evolution of the Duobuza deposit, a typical porphyry Cu-Au deposit, using the sulfur isotope composition of sulfides in successive hydrothermal stages. We show (1) an increase of δ³⁴S values from the inner potassic core (−4.8 to −0.4‰, <i>n</i> = 37) to the peripheral propylitic halo (1.2 to 4.8‰, <i>n</i> = 5) during the early stage; (2) an increase from the early stage potassic alteration to the transitional stage sericite-chlorite alteration (−2.6 to 0.6‰, <i>n</i> = 25); (3) a progressive enrichment, from the quartz-dominated veins (−3.1 to 0.5‰, <i>n</i> = 10), through the anhydrite-dominated veins (−2 to 0.6‰, <i>n</i> = 7), and to the pyrite-dominated veins (−0.7 to 2.3‰, <i>n</i> = 7) during the late stage. The integration of sulfur and oxygen isotope and fluid inclusion data, modeling and mineralogical evidence suggests that the ³⁴S depletion within the potassic core compared to the propylitic halo can be best explained by boiling-induced oxidation of hydrothermal fluids. The increase in δ³⁴S from potassic alteration, through sericite-chlorite alteration, to the late stage hydrothermal veins is interpreted to be related to the partial reduction of an oxidized fluid by water-rock interaction. Our findings highlight the potential of sulfur isotope data to assist exploration for Cu-Au porphyry deposits where a predictable zonation pattern is present.</p>