Abstarct: The purpose of this study was to evaluate the concentration and speciation of potentially toxic elements in sediments of Karoon River in Ahvaz city district. For this purpose, 14 surface samples (0-5 cm) were collected. After acidic digestion of samples, total concentration of major and trace elements was determined by ICP-OES instrument. Also, a five stage procedure of sequential extraction was used to investigate the speciation and fractionation of potentially toxic elements. The obtained data were analyzed using geochemical indices. The obtained results show that the pH of the sediments is in the neutral to alkaline range. The amount of organic matter in the sediments ranges from 0.4 to 4.9%. The cation exchange capacity of the samples varies between 5.4 to 12.6 meq/100 gr. The average concentration Cr in the sediments is higher than the respective international values. On the basis of enrichment factor values, the sediment are moderately enriched with Cd. According to the Igeo values, the study sediments are classified as non-polluted to slightly polluted. According to the ecological risk index classification, sediments of Karun River are moderately contaminated with Cd. Also, baxsed on the sequential extraction results, the studied elements are mainly present in the non-residual phases; therefore, they are bioavailable and accessible. Compared to other elements, the mobility of Cd, Mn, Pb and Zn are higher.