The objective of this study was to characterize the bioactive ingredients and antiulcer effects of Lactuca sativa leaves. Several bioactive chemicals were found in the cold methanolic extract of Lactuca sativa leaves after gas chromatography-mass spectrometry (GC-MS) research: 9,12-octadecadienoic acid (Z,Z)-, cyclononasiloxane, octadecamethyl-, n-hexadecanoic acid, Hexadecanoic acid, 2-hydroxy-1-(hydroxymethyl)ethyl, octadecanoic acid, 2-hydroxy-1-(hydroxymethyl)ethyl ester, 9-octadecenamide, (Z)-, hexadecanoic acid, stigmasterol, benzothiazole, ethyl iso-allocholate, and octacosane. Distinct fingerprint regions in GCMS indicated the existence of bioactive compounds. The leaf powder of Lactuca sativa (LPL) demonstrated substantial antiulcer properties at 400 mg/kg, which was almost equivalent to the standard drug at 20 mg/kg. The cytokine network was efficiently regulated by reducing the production of proinflammatory cytokines such as IL-1, IL-6, and TNF-. The levels of caspase-3 and caspase-9 were also considerably lowered at p < 0.05 significant level.