Lung cancer, one of the most common cancer is a cause of concern associated with cancer-related mortality. Benzo[a]pyrene [B(a)P], a potent carcinogen as well as an environmental contaminant is reported to be found in cigarette smoke among various sources. The present study focuses on the chemopreventive potential of Diosmin against B[a]P-induced lung carcinogenesis and its possible mechanism in male Swiss Albino mice (SAM). SAM were treated orally with Diosmin (200 mg/kg b.w.) for 16 weeks and/or B[a]P (50 mg/kg b.w) for a period of 4 weeks. B[a]P treated cancerous mice showed increased peroxidation of membrane lipid as well as a decrease in the level/activity of antioxidant proteins. Cancerous mice also showed an increased level of carcinoembryonic antigen (CEA) and neuron-specific enolase (NSE). Diosmin treatment, however, leads to decreased peroxidation of lipids, increased antioxidant proteins as well decrease in the level of CEA and NSE. B[a]P-induced cancerous animals also exhibited increased expression of cyclic AMP response element-binding protein (CREB), COX2 as well as prostaglandin-E2 (PGE2) while Diosmin-treated mice were found to have an ameliorative effect. Histopathological results further confirm the protective effect of Diosmin in averting B[a]P-induced pathological alterations of lung tissue. Overall, our results suggest Diosmin exerts its chemopreventive potential possibly via targeting the CREB/cyclooxygenase-2 (COX-2)/PGE2 pathway thereby repressing inflammation.