【Objective】 Aiming at the common problem of arsenic (As) /cadmium (Cd) pollution and declining soil fertility in paddy fields in South China, organic manure is used to improve soil fertility, while dissolved organic carbon (DOC) is amended as metabolic substrate for sulfate-reducing bacteria to promote reduction of SO₄^2- into S^2- and subsequent formation of As/Cd sulfide deposit in flooded soil. This way of thinking may provide a useful solution to the common problem.【Method】 A systematic research was carried out to analyze effects of organic manure (OF) and amendment of sulfate (SOF) on solubility, bioavailability and chemical conversion of As and Cd in As/Cd compound polluted paddy soil.【Result】 Treatment OF (application of organic manure) reduced the concentration of As(III) in soil porewater by 9%~64% and increased that of Cd in porewater by 4~12 times during the first 10 weeks of flooding, as compared to CK. Sequencing extraction of solid As/Cd by fraction shows that Treatment OF increased the content of amorphous hydrous Fe oxides-bonded As, low in environmental stability, and specifically-sorbed As by 4%~5% and reduced soil Fe oxide-Cd and carbonate-Cd by 55% and 11%, respectively. Treatment SOF (application of organic manure amended with sulphate) did not have much effect of reversing solubility and transformation of soil As/Cd between solid fractions, but did promote reduction of SO₄^2- into S^2- that raised the content of soil arsenic sulfite by 71%. The pot experiments done in the research show that Treatment OF reduced As accumulation in the stems and roots of rice seedlings by 44%~ 47%, but increased total As in brown rice and inorganic As in white rice at the mature stage by 22% and 12%, respectively. And Treatment OF significantly enhanced Cd accumulation in rice seedlings and multiplied Cd content in brown rice Cd by 1.2 times. Treatment SOF significantly reversed the trend of Treatment OF increasing As content in brown rice, but did not have much effects on Cd accumulation in brown rice and increase in inorganic As in white rice.【Conclusion】 Application of organic manure has a serious risk of increasing As/Cd accumulation in rice, and even amendment of sulfate has only some mild effect of controlling bioavailability of soil As/Cd. Therefore, the potential threat of application of organic manure to quality and security of rice cultivated in As/Cd contaminated paddy fields has aroused great concerns.