Objective:To study the changes in serum small molecule metabolites after brucella infection in humans using untargeted metabolomics methods, and screening representative biomarkers. Methods:A total of 109 serum samples collected from January 2019 to December 2021 at the Brucellosis Clinic of the Baotou Center for Disease Control and Prevention were divided into acute phase group ( n = 40), chronic phase group ( n = 35) of brucellosis, and healthy group ( n = 34) based on clinical diagnosis. Ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry technology was used to test serum samples and screen for differential metabolites. Receiver operating characteristic curve was used to evaluate the predictive ability of differential metabolites for brucellosis. Enriched pathways were screened using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway to identify metabolic pathways significantly affected. Results:A total of 17 differential metabolites were screened between the acute phase group and the healthy group, and 12 differential metabolites were screened between the chronic phase group and the healthy group. There were a total of 5 differential metabolites (oleamide, linoleamide, stearamide, palmitoleic acid, α-linolenic acid) statistically significant among the three groups ( F = 16.84, 17.52, 14.31, 13.01, 20.76, P < 0.05). KEGG pathway analysis showed that the differential metabolites in the acute phase group were enriched in metabolic pathways such as ether lipid metabolism, glycerophosphate metabolism, sphingolipid signal and sphingolipid metabolism. The differential metabolites in the chronic phase group were enriched in metabolic pathways such as glycerophosphate metabolism, ether lipid metabolism, protein digestion and absorption metabolism. Conclusion:Untargeted metabolomics methods can screen out serum small molecule metabolites that undergo changes after brucella infection in the human body, including oleamide, linoleamide, stearamide, palmitoleic acid, α-linolenic acid can serve as potential biomarkers to distinguish brucellosis patients from healthy people.