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Different sample pretreatment extraction techniques and analytical methods are often used for nitrate determination in vegetables; however, the effects of these variables have not been properly examined. Therefore, sample pretreatment (oven-dried and fresh extraction) and nitrate determination methods (colorimetric method (salicylic method (SM)) and high-performance liquid chromatography (HPLC) were compared in Chinese kale (K) and morning glory (M) in this study. Oven-dried and fresh samples (K and M) were extracted by maceration and determined for nitrate content by the SM. As a result, the nitrate contents of both the oven-dried samples were significantly lower than the fresh samples (p < 0.01). A high correlation between the SM and HPLC was observed in 21 oven-dried samples of K and M. The nitrate contents using SM were significantly lower than the HPLC (p < 0.01). Both methods could be used for nitrate analysis in vegetables with an awareness of impurities in the SM. HIGHLIGHTS The drying process reduced the nitrate content Temperature effects nitrate content The SM demonstrated a lower nitrate content than the HPLC in all the dried vegetable samples Colorimetric by Salicylic acid and HPLC method could be used for nitrate analysis in vegetables GRAPHICAL ABSTRACT