In the present work, thiourea-formaldehyde (TUF) chelating resin was synthesized and used in the adsorptions of selenite (SeO The effects of initial acidity and initial selenium concentrations on the adsorptions were examined by batch technique. The synthesized resin was applied to the elemental analysis to determine its composition. FT-IR spectra and SEM/EDS were also recorded before and after selenite adsorption. It was found that selenite and selenate ions were adsorbed onto TUF resin at strong acidic conditions (3-5M HCl). The adsorption capacities of the resin were calculated as 833.3 mg g À1 TUF resin for selenite ions and 526.3 mg g À1 TUF resin for selenate. All the adsorption data obtained for both selenite and selenate ions fitted well to the Langmuir isotherm. It was seen that the adsorption mechanisms in the both adsorptions were governed by the reduction of selenite or selenate to elemental selenium, Se