Lung cancer is the leading cause of cancer death worldwide and its clinical management remains challenge. Here, we repurposed antibiotic levofloxacin for lung cancer treatment. We show that levofloxacin is effectively against a panel of lung cancer cell lines via inhibiting proliferation and inducing apoptosis, regardless of cellular origin and genetic pattern, in in vitro cell culture system and in vivo xenograft lung tumor model. Mechanistically, levofloxacin inhibits activities of mitochondrial electron transport chain complex I and III, leading to inhibition of mitochondrial respiration and reduction of ATP production. In addition, levofloxacin significantly increases levels of ROS, mitochondrial superoxide and hydrogen peroxide in vitro and oxidative stress markers (HEL and 4-HNE) in vivo. Antioxidants, such as NAC and vitamin C, prevent the inhibitory effects of levofloxacin, confirming the induction of oxidative damage as the mechanism of its action in lung cancer cells. Our work demonstrates that levofloxacin is a useful addition to the treatment of lung cancer. Our work also suggests that targeting mitochondria may be an alternative therapeutic strategy for lung cancer treatment.