<p>Cerium isotopes (δ^142/140Ce) are a promising proxy for reconstructing the evolution of Earth redox conditions over geological time, but their fractionation in anoxic-sulfidic environments remains poorly understood. Here, we present the first δ^142/140Ce data from anoxic-sulfidic sediments of the South China Sea. Our results show that no significant Ce anomalies (0.92–1.01) are observed in anoxic-sulfidic sediments. In addition, the δ^142/140Ce values (−0.007‰–0.070‰) were found to be lower than those observed in oxic environments, yet comparable to values of the upper continental crust. This phenomenon may be attributed to the reductive dissolution of Fe and Mn (oxy)hydroxides in a reducing environment, resulting in the release of heavy ¹⁴²Ce into the water. Additionally, Ce is predominantly dissolved and rarely occurs in the sediments. These observations indicate that the Ce in anoxic-sulfidic sediments predominantly originates from terrigenous detritus supply, exhibiting a limited authigenic component, and the δ^142/140Ce values predominantly reflect the terrigenous detritus value. Consequently, although Ce isotopes can distinguish between oxic and anoxic-sulfidic conditions, their quantitative application as a paleoredox proxy in sulfidic environments requires direct constraints on authigenic Ce isotopic compositions.</p>