In this study, the influence of organic matter on As(V) adsorption onto clay minerals was evaluated through batch experiments using three solid phases: crude kaolinite, humic acid (HA)-coated kaolinite and heavy oil cut (HOC)-coated kaolinite. In all cases, the adsorption isotherms fitted the Freund equation. Adsorption onto the coated kaolinites was significantly higher than onto the crude kaolinite, with the type of organic matter coating playing a determining role in this increased adsorption.Des experiences d'adsorption d'arsenic As(V) en reservoirs fermes ont ete realisees sur trois types de solides (des kaolinites vierges, des kaolinites recouvertes d'acides humiques (AH) et des kaolinites recouvertes de fuel lourd [FL]), de facon a determiner le role de matiares organiques de natures differentes sur cette adsorption. Les isothermes obtenues suivent une equation de Freundlich; on observe la sequence d'affinite de As pour les solides : kaolinite < kaolinite-AH < kaolinite-FL. La presence de matieres organiques a la surface de la kaolinite augmente significativement l'adsorption de As. La nature de la matiere organique adsorbee est un des parametres cles de cette augmentation.