ObjectiveSerum metabolomics of acute lung injury（ALI） in rats was conducted using ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry（UPLC-Q-TOF-MS） to explore the similarities and differences in the mechanism of Qingqiao（harvested when the fruits of Forsythiae Fructus were initially ripe and still green in color） and Laoqiao（harvested when the fruits of Forsythiae Fructus were ripe） in the treatment of ALI. MethodA total of 24 SD male rats were acclimatized and fed for 1 week， 6 of them were randomly selected for the blank group and 18 for the experimental group. The ALI model was induced in the experimental group by tracheal intubation with lipopolysaccharide（LPS）. After successfully constructing the ALI model， these rats was randomly divided into model group， Qingqiao group and Laoqiao group， with 6 rats in each group. The Qingqiao and Laoqiao groups were administered orally once a day at a dose of 1.5 g·kg^-1， while the blank and model groups received an equivalent volume of saline for 3 consecutive days. The pathological conditions of rat lung tissues were comprehensively assessed by hematoxylin-eosin（HE） staining， wet-to-dry mass ratio（W/D） of lung tissues， and protein concentration in rat bronchoalveolar lavage fluid（BALF）. The levels of interleukin（IL）-6， IL-1β and tumor necrosis factor（TNF）-α in BALF were quantified using enzyme-linked immunosorbent assay（ELISA）. UPLC-Q-TOF-MS was used to identify and analyze the chemical compositions of Qingqiao and Laoqiao， and serum metabolomics of rats in each group was analyzed， combined with multivariate statistical analysis with variable importance in the projection（VIP） value>1， P<0.05 from t-test， and fold change（FC）≥1.5 or FC≤0.5 to screen the differential metabolites Qingqiao and Laoqiao for the treatment of ALI. The Kyoto Encyclopedia of Genes and Genomes（KEGG） database was used in combination with MetaboAnalyst for the metabolic pathway analysis of the screened differential metabolites. ResultCompared with the blank group， rats in the model group exhibited enlarged alveolar lumen， ruptured alveoli， interstitial hemorrhage， bronchial exudation of a large number of neutrophils and erythrocytes， and a significant increase in the protein concentration in the BALF and the W/D value of the lung tissues（P<0.01）. In contrast， compared with the model group， rats in the Qingqiao group and the Laoqiao group showed reduced bronchial hemorrhage in the lungs， and the protein concentration in the BALF and the W/D value of the lung tissues were significantly decreased（P<0.01）， the lung injury was significantly alleviated， but more obvious in the Qingqiao group. Compared with the blank group， the expression levels of IL-6， IL-1β and TNF-α in the BALF of the model group were significantly higher（P<0.01）. Additionally， compared with the model group， the expression levels of IL-6， IL-1β and TNF-α in the Qingqiao and Laoqiao groups were significantly lower（P<0.01）. The chemical composition analysis of Qingqiao and Laoqiao revealed that 63 components were detected in Qingqiao and 55 components were detected in Laoqiao， with 47 common components， 16 components unique to Qingqiao and 8 components unique to Laoqiao. Characterizing the differences in serum metabolomics in rats， 19 and 12 metabolites were called back by Qingqiao and Laoqiao， respectively. The metabolic pathway enrichment analysis showed that Qingqiao exerted its therapeutic effects by affecting 6 key metabolic pathways， including linoleic acid metabolism， phenylalanine metabolism， phenylalanine， tyrosine and tryptophan biosynthesis， glycerophospholipid metabolism， α-linolenic acid metabolism， and arachidonic acid metabolism， and Laoqiao exerted therapeutic effects by affecting 6 key metabolic pathways， including linoleic acid metabolism， arachidonic acid metabolism， sphingolipid metabolism， phenylalanine metabolism， ascorbate and aldarate metabolism， and glycerophospholipid metabolism. ConclusionQingqiao and Laoqiao have therapeutic effects on ALI， and Qingqiao is more effective. Both of them can play a therapeutic role in ALI by regulating amino acid metabolism and lipid metabolism， but the metabolic pathways affected by them are different.