In this study, we applied X-ray absorption near-edge structure spectroscopy (XANES) to the determination of the As-III/ As-V ratios in sediments in the Bengal Basin, where groundwater contamination of As causes serious health hazard. The depth profile of oxidation state of As in sediment shows that As-III is dominant species in the depth where As concentration of groundwater is high. This result is consistent with the general understanding about mobility of inorganic As species in various field observations.