The chemopreventive efficacy of baicalein (BE) flavanoid during benzo(a)pyrene [B(a)P]-induced lung carcinogenesis was investigated in Swiss albino mice. Lung cancer was induced by 50mg/kg body weight of B(a)P, given orally twice a week for 4 successive weeks in male Swiss albino mice. B(a)P-induced mice were pre- and post-treated with 12mg/kg body weight of BE, given orally once in a week for 16 weeks. After the experimental period, protein carbonyl content, total iron levels, reactive oxygen species (ROS) generation, DNA unwinding, levels of thiobarbituric acid reactive substances (TBARS), hydro-peroxides (OH) and glycoproteins (hexose, hexosamine and sialic acid) were found to be increased in the lung of B(a)P-induced mice. Accompanied by the activities of enzymic antioxidants [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST)], non-enzymic antioxidants (reduced glutathione, vitamin C, vitamin E and vitamin A), membrane bound ATPases (Na⁺/K⁺ ATPase, Mg²⁺ ATPase and Ca²⁺ ATPase) were found to be decreased due to induction of lung cancer in mice. Treatment (pre- and post-) with BE significantly ameliorated all these above alterations. The chemopreventive action observed in the present study is attributed to the antioxidant potential and free radical scavenging properties of BE against lung carcinogenesis in Swiss albino mice.