Abstract: To investigate the contents of small-molecule aldehydes in smokeless tobacco products, such as formaldehyde, acetaldehyde, propionaldehyde, acrolein, butyraldehyde and crotonaldehyde, these targets and their internal standards were extracted under ultrasound and derived with 2, 4-dinitrophenylhydrazine(DNPH) simultaneously by a water-isohexane biphase system. The derivatives were then analyzed by Q-Exactive mass spectrometry with ultra-performance liquid chromatography-high resolution mass spectrometry(UPLC-HRMS) method. The result showed that:1)Preparation time was less than 30 min after optimization, and analysis time was reduced to 6 min by adopting C₁₈ UPLC column. 2) The interferences of acetone and butanone to propionaldehyde and butyraldehyde were excluded by using characteristic secondary ion for quantitative analysis. 3)The linear ranges of analytes were over two orders of magnitude with good correlation coefficients (R²>0.99), the limits of quantification ranged from 0.07 to 0.90 ng/mL, and the recoveries were in the range of 81.1%-107.6% with relative standard deviations no more than 12.7%. 4)Formaldehyde and acetaldehyde were major small-molecule aldehydes in smokeless tobacco products. The established method is simple, rapid and reliable, it is suitable for the analysis of small-molecule aldehydes in smokeless tobacco products.