A simple and reliable method for rapid and selective separation and determination of trace amounts of Ce3+ ions from aqueous samples using octadecyl-bonded silica membrane discs modified with 1,3,5-trithiacyclohexane (TTCH) and spectrophotometry with arsenazo(III) is presented. Extraction efficiency and the influence of sample matrix, pH of sample solution, type and minimum amount of stripping acid, and flow-rates were investigated. The maximal capacity of the membrane discs modified with 15 mg of TTCH was found to be 547 mug of cerium. The limit of detection of the proposed method is 2 ng/mL. The effects of various cationic interferences on the percent recovery of cerium in binary mixtures were studied. The method. was applied to the recovery of Ce3+ ions from synthetic samples.