Mitigation of arsenic (As) accumulation in rice is imperative to pursue globally to decrease human threat from As-laden rice consumption. Intermittent flooding constitutes a successful measure in reducing As-grain level; however, it is an uncommon practice for rice production in Asia as compared to continuous flooding and can limit rice yield. Arsenite (As^III)–natural organic matter (NOM) complexes under strong reducing conditions have been documented as an effective mechanism for As sequestration in terrestrial wetlands, yet the contribution of NOM on As bioavailability in the soil-plant system remains unresolved. Herein, we examined the effects of organic sulfur (manure) and inorganic sulfur (sulfur powder) on As bioavailability in an As-laden soil and rice grown under continuously flooded conditions. Soil incorporation of organic and inorganic sulfur materials significantly (p<0.05) decreased As^III concentration in grain by 65% and 61%, respectively. The As solubility data revealed that As associated with sulfides and resistant minerals were the dominant As pools in the sulfur-amended soil, demonstrating the formation of As sulfides using reductive precipitation. Our results shade light on the potential use of sulfur materials in decreasing grain As concentration under continuous anaerobic conditions. Moreover, such flooded conditions efficiently promote the metal sulfide precipitates, which advocate the proper water management regimes for reducing grain Cd level in contaminated soils. The combined use of sulfur material with continuous flooding management is proposed to be a promising practice to diminish both As and Cd levels in rice grown in As/Cd co-contaminated soils.