Background: Corilagin is vastly found in plants and incorporated in countless traditional medicinal systems to treat various ailments including cancer disease. However, till now, no scientific study has been done to validate its efficiency with appropriate experimental evidence. Resulting, this study examined the ameliorative effects of corilagin in benzo(a)pyrene (B[a] P)-induced lung cancer in vivo. Methods: Experimentally, the B(a)P (50 mg/kg body weight [b.wt.]) was administered orally to initiate lung cancer in mice, and the supplementation of prophylactic and therapeutic treatment by corilagin (30 mg/kg b.wt.) was observed for changes in b.wt. and lung weight, tumor incidence, oxidative stress marker (lipid peroxidation), tumor markers (carcinoembryonic antigen, neuron-specific enolase, aryl hydrocarbon hydroxylase, lactate dehydrogenase, γ-glutamyl transpeptidase, 5′-nucleotidase, alpha-keto dehydrogenase, citric acid cycle enzymes isocitrate dehydrogenase, succinate dehydrogenase, and malate dehydrogenase), histological and immunohistochemical analysis (proliferating cell nuclear antigen), and apoptotic mRNA gene expression (Bax, Bcl-2, caspase-3, caspase-9, and cytochrome-c). Results: B(a)P-induced animals exhibited unusual changes in b.wt. and lung weight, tumor incidence, oxidative stress marker, enzymatic antioxidants, tumor markers, histological lung tissue damage, number of proliferating cell nuclear antigen, and apoptotic mRNA gene expression. On prophylactic and therapeutic treatment of corilagin, the animals showed reinstatement of all the above alterations to the near normal. Conclusion: These findings of all the analyzed data demonstrate that the B(a)P-induced animals of pre- and post-treated with corilagin may prevent initiation of lung cancer, hence establishing its chemopreventive effect against lung tumorigenesis.