In this study, a simple, rapid, precise and sensitive high performance liquid chromatography (HPLC) method using an UV detector was developed for the determination of nitrate and nitrite amounts in vegetables. The optimal conditions were found and applied using 0.01 M octylammonium orthophosphate of aqueous 30% (v/v) methanol of pH 7.0 for the mobile phase at flow rate of 0.8 mL/min. The total time for one sample analysis was within 10 min. Recoveries of nitrate and nitrite were between 96.6% to 105.7%. The calibration curves of nitrate and nitrite were extremely linear, where both correlation coefficients were greater than 0.9990 in the range of 0.1~100.0 µg/mL. Therefore, this HPLC method is applicable for simultaneously determining the nitrate and nitrite levels in vegetables. For application, nitrate and nitrite amounts in 12 marketed vegetables were determined by this HPLC method. The results showed nitrate and nitrite contents varied in a range of 225~4,410 mg/kg and <5~200 mg/kg, respectively.