Inorganic anions were determined as triiodide by postcolumn reaction with iodide under an acidic condition with help of alpha-cyclodextrin in ion chromatography. Analytes reacting with iodide to produce iodine could be determined by the present method. The analytes were indirectly detected at 287 or 355 nm. The presence of alpha-cyclodextrin caused an increase in the concentration of triiodide, leading to improvement of the sensitivity. The present system achieved good selectivity to iodate, bromate and nitrite as well as good repeatability under the optimum conditions. The determination of nitrite in river water was possible.