The liver kinase B1 (LKB1) gene is a tumor suppressor associated with the hereditary Peutz-Jeghers syndrome and frequently mutated in non-small cell lung cancer and in cervical cancer. Previous studies showed that the LKB1/AMPK axis is involved in regulation of cell death and survival under metabolic stress. By using isogenic pairs of cancer cell lines, we report here that the genetic loss of LKB1 was associated with increased intracellular levels of total choline containing metabolites and, under oxidative stress, it impaired maintenance of glutathione (GSH) levels. This resulted in markedly increased intracellular reactive oxygen species (ROS) levels and sensitivity to ROS-induced cell death. These effects were rescued by re-expression of LKB1 or pre-treatment with the anti-oxidant and GSH replenisher N-acetyl cysteine. This role of LKB1 in response to ROS-inducing agents was largely AMPK-dependent. Finally, we observed that LKB1 defective cells are highly sensitive to cisplatin and γ-irradiation in vitro, suggesting that LKB1 mutated tumors could be targeted by oxidative stress-inducing therapies.