Background: The diagnosis, severity assessment, and development of therapeutic strategies for asthma are crucial aspects of disease management. Since biomarkers are reliable tools in disease management, we aimed to identify and explore asthma-associated biomarkers and investigate their mechanisms.Methods: Lipidomics was used to profile serum glycerophospholipids in asthmatic patients and controls. The absolute concentration of lysophosphatidylglycerol (LPG) 18:0 was quantified in various asthma subtypes. Mouse asthma models were used to confirm its potential as a biomarker and investigate its mechanismsin vivo.The effects of LPG 18:0 on CD4⁺T-cell differentiation, proliferation and apoptosis were assessedin vitroby flow cytometry, while mitochondrial dysfunction was evaluated through mitochondrial membrane potential, reactive oxygen species and ATP production measurements. The intracellular mechanism of LPG 18:0 in regulatory T-cells (Tregs) was investigated using small-molecule inhibitors.Results: The serum glycerophospholipid profile varied between asthmatic patients and control group, with LPG 18:0 levels being notably higher in asthmatic patients, correlating with asthma severity and control level.In vivoandin vitrostudies revealed that LPG 18:0 impaired naïve CD4⁺T-cell differentiation into Tregs and compromised their suppressive function. Further investigation demonstrated that LPG 18:0 treatment reduced the FOXP3 protein levelviaSIRT1-mediated deacetylation during Treg differentiation.Conclusions: This study identifies that serum levels of LPG 18:0 are generally elevated in asthmatics and serve as a biomarker for asthma. LPG 18:0 impairs Treg functionviathe NAD⁺/SIRT1/FOXP3 pathway. Our research reveals the potential of LPG 18:0 as a biomarker for asthma, elucidating its role in asthma diagnosis and treatment.