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Acid stress restricts the viability and probiotic functions of lactic acid bacteria during production applications. Therefore, studying the potential acid tolerance mechanisms of a specific strain is crucial for its further application. This study first examined the influence of decreasing acidity on the growth of Lentilactobacillus kefiri IMAU10804, a slow-growing milk rod bacterium. Subsequently, this study used liquid chromatography-mass spectrometry (LC-MS) to analyze the metabolomics differences in L. kefiri IMAU10804 before and after acid stress. Results showed that the growth of L. kefiri IMAU10804 was inhibited with decreasing pH. When L. kefiri IMAU10804 was treated under pH 3. 0 for 60 min, 796 and 615 metabolites were detected in positive and negative ion modes, respectively. Multivariate statistical analysis was performed using SIMCA 14. 1 software combined with Metaboanalyst 5. 0, revealing that a large number of metabolites were enriched in metabolic pathways, such as ABC transporter, arginine and proline metabolism, and purine metabolism. Based on the criteria of P < 0. 05, variable importance in projection score ≥ 1, and fold change ≥ 1. 5, 24 major differential metabolites were found, including L-proline, aspartic acid, and trehalose. This study demonstrated significant changes in the growth and metabolism of L. kefiri IMAU10804 under acid stress environment, providing data support for the subsequent development and application of lactic acid bacteria products. [ABSTRACT FROM AUTHOR]