Contamination of paddy soils with Cd and the subsequent production of Cd-contaminated rice grains are the main sources exposing Cd pollution to the food chain globally. Paddy fields are characterized with periodic flooding and drainage, which have a substantial impact upon the solubility of Cd in soils. The elevated Cd concentrations in rice grains are mainly attributed to the enhanced mobilization of Cd during pre-harvest drainage, with this period coinciding with grain filling stage. There are substantial variations among the soils in the release rates of Cd once soils are drained, but the underlying mechanisms remain unclear. In this study, we used sulfate-reducing bacteria (SRB) to synthesize Cd and Zn sulfides with different Zn/Cd ratios (0-600 on a molar basis). Using a microcosm incubation system simulating the occurrence of typical flooded/drained processes, we added these synthetic sulfides into the flooded soils to investigate the release of Cd in the subsequent oxidation process. Our results show that a higher Zn/Cd ratio leads to a lower Cd release during the oxidation phase under different pH conditions. When the Zn/Cd ratio is higher than 200, little of Cd is released. These results indicate an important role of the ratio of Zn/Cd in sulfides formed in the reducing soil in the subsequent release of Cd during soil drainage. Enhancing the ratio of Zn/Cd in the sulfides may provide a strategy to mitigate Cd accumulation in rice grains.