Arsenic (As) accumulation in rice grains poses critical health risk for populations whose staple food is rice. Organics could affect As transformation and volatilization in soil, and subsequently affect As accumulation and speciation in rice grains. Straw application significantly promoted As release from soil and As methylation, also enhanced As volatilization from soil. However, straw application significantly increased DMA accumulation in polished rice grains. Straw biochar application significantly decreased inorganic As concentration in polished grains, but did not significantly affect As methylation and DMA accumulation. Fulvic acid addition significantly increased As bio-availability in the soil, and high level of humic acid addition significantly enhanced As volatilization.