Over a hundred million people across the globe are chronically exposed to high levels of Arsenic (As) in shallow reducing groundwaters utilized for drinking, cooking and irrigation. The importance of the role of degradable organic matter (OM) is widely recognized in As mobilization by microbially mediated reductive dissolution of iron (Fe-III) hydrated oxides/hydroxides and/or reduction of As(V). However, the role that organics play in As release in high-As aquifers remains ambiguous in many regions. Initial results of the organic analysis of the hydrocarbon fractions of sediments obtained from SW Taiwa (Yichu) and the Red River Delta, Vietnam (Van Phuc Village) revealed an influx of mature OM source in these sediments. The mechanism and the controlling factors on the release of As from these sediments are investigated.