Objective：This study aims to explore the role of peptides in lung adenocarcinoma and its potential molecular mechanisms through peptideomics analysis. Methods：Endogenous peptides from 3 pairs of age-matched male lung adenocarcinoma and paracancerous tissues were extracted and detected by liquid chromatography-tandem mass spectrometry（LC-MS/MS）. Bioinformatics was used to infer the potential functions of differential peptides. CCK-8 assays，wound-healing assays，and Transwell assays were carried out to verify the effect of key peptides on the malignant phenotype of lung adenocarcinoma cell lines（A549，H1975）. Results：A total of 4 538 peptides were identified，of which 242 were differentially expressed（fold change≥2.0，FDR<0.05），corresponding to 202 precursor proteins. GO analysis and KEGG pathway enrichment analysis showed that these proteins were closely related to a series of important biological activities of tumorigenesis and development. Additionally，the novel peptide LACRP2 was also focused on. It was confirmed that this peptide could inhibit some malignant phenotypes of lung adenocarcinoma cell lines in vitro. Conclusion：The endogenous peptide LACRP2 may be related to some malignant phenotypes of lung adenocarcinoma. Peptidomics can aid in understanding the pathogenesis of lung cancer more comprehensively.