Abstract: The impacts of the regulation of sulfur (S) metabolism in vivo on arsenic (As) and S species and on As accumulation by Pteris vittata L. were investigated using a synchrotron-based X-ray-absorption fine structure method. The S assimilation inhibitor l-buthionine-sulfoximine (BSO) markedly inhibited As reduction, doubling arsenate (As(V)) content in P. vittata rhizoids. The resulting As transport blockage in rhizoids, decreased As movement to aboveground tissues by 47%. The significant impact of BSO demonstrated the vital role of sulfhydryl groups (ductants in As(V) reduction and confirmed the importance of As(V) reduction in As accumulation in this fern. The S metabolism accelerant O-acetyl-l-serine resulted in the appearance of large amounts of As–SH in rhizoids and had no obvious impact on As accumulation, but with As stress conditions, effectively increased plant biomass, possibly through chelation of excess As with ed able to act as both a reductant and a chelator of As in P. vittata, and the ratio of may have been a factor that determined the specific role of :italic>P. vittata under these conditions. [Copyright &y& Elsevier]