Synchrotron radiation extended X-ray absorption fine structure (SR EXAFS) was used to study the transformation of coordination and redox state of arsenic (As) in a newly discovered As hyperaccumulator, Pteris vittata L., which is considered to have great potential for phytoremediating the As contaminated soil. It is shown that the As in this plant was mainly coordinated with oxygen in the reduced state, As (Ⅲ), and the reduction of As (V) occurred in the root after it was taken up. No oxidation of As (Ⅲ) was found during the translocation of As, from root to shoot. Only a small amount of As was coordinated with sulfur in root and petiole, but not distinct in pinna.