A novel approach for the simultaneous separation and indirect ultraviolet detection of chlorate and perchlorate using pyridinium ionic liquids as mobile phase additives in reversed-phase liquid chromatography was developed. Pyridinium ionic liquids and imidazolium ionic liquids as the mobile phase additives were compared. The effects of pyridinium ionic liquids, methanol, column temperature, and detection wavelength on the separation and detection of chlorate and perchlorate were investigated. The role of ionic liquids, retention rules and relevant mechanisms were discussed. Pyridinium ionic liquids mainly acted as ultraviolet absorption reagent and ion-pair reagent. The successful separation and indirect ultraviolet detection of chlorate and perchlorate were achieved by using a common reversed-phase column, 0.2 mmol/L N-octylpyridinium bromide aqueous solution/methanol (90/10, v/v) as mobile phase and at the detection wavelength of 210 nm. The retention times of chlorate and perchlorate were 30.51 and 37.06 min, respectively. The detection limits of chlorate and perchlorate were 0.16 and 0.29 mg/L, respectively. The linearity and repeatability of the method were satisfactory. The approach was used to the analysis of river water samples with accurate and reliable results. This method is easy to popularize due to the use of common reversed-phase column and ultraviolet detector in liquid chromatography.