Abstract: In order to clarify the influence of acute hypobaric hypoxia on the bile acids of the rat small intestine, we used ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to identify bile acids in the contents of the small intestine from untreated and acute hypobaric hypoxia-treated rats. Thirty-nine bile acids were detected; PCA and OPLS-DA analysis revealed marked differences in the composition of bile acids between the untreated and the acute hypobaric hypoxia groups. Bile acids were screened with VIP > 1,|log₂FC|≥ 1, P < 0.05, and a total of 7 bile acids with significant differences in content between the two groups were obtained, including 5 conjugated bile acids, 2 unconjugated bile acids; in addition, the content of conjugated bile acids has risen in the treated group. This study demonstrated the influence of high-altitude hypoxic environment on bile acid composition and metabolism in rats. All the animal experiments in this study were approved by the 940th Hospital Ethics Committee (approval No:2020KYLL012).