ABSTRACT. Ketamine is a dissociative anesthetic agent that has been widely used in surgery and for relieving pain in chronic cancer patients. We applied ketamine to breast cancer cell line MDA-MB-231 to detect the effect of treatment and molecular mechanisms involved. We found that ketamine can upregulate the level of anti-apoptosis protein Bcl-2, which promotes breast cancer cell invasion and proliferation. Knockdown of Bcl-2 could inhibit the increase of Bcl-2 and reduce the invasion and proliferation caused by ketamine in human breast cancer cells. Our findings provide new insight into the effects of ketamine in cancer treatment; we suggest that ketamine, which has been widely used in cancer operations and for relieving pain in chronic cancer patients, may be not the best choice because it can worsen the cancer through promotion of anti-apoptosis.