An experiment using the rhizo-bag system and the sequential extraction method was conducted to investigate translocation and transformation of arsenic during the whole rice growing period and analyze As fractions in a soil-rice system，where the soil was moderately-slightly contaminated with arsenic.Results show that the concentrations of total arsenic as well as amorphous and poorly-crystalline hydrous arsenic oxides in the rhizosphere (R) were significantly higher than those in the nonrhizospheric soil (NR) during the third and fourth growth periods，while the concentration of residual arsenic，the lowest in availability，were lower in the rhizosphere (R) than in the nonrhizospheric soil (NR).The iron plaques over the surface of roots were dominantly formed of well-crystallized hydrous oxides of Fe and Al and amorphous and poorly-crystalline hydrous oxides of Fe and Al (＞90%).Moreover，during the fast growing period，the iron plaques aged the most and their arsenic adsorption capability decreased by 60% and by 10% as compared that in the first and second growing periods，respectively，however，it did not vary completely with the change in quantity of the iron plaques，but was closely related to fractions of Fe in the iron plaques.The behaviors of arsenic in the soil-rhizosphere-rice(YY-1) system could be concluded as follows：arsenic transported from bulk soil to rhizosphere with iron oxides reducing in soil and accumulated in the oxidizing rhizosphere.Iron plaques increased arsenic uptake by roots during the early growth periods，while it functioned as buffer in arsenic uptake for decreasing concentrations of arsenic in rice roots during the last three growth periods.