The influence of surgery and anesthesia on aspects of malignant tumor has received considerable attention in recent years. It is suggested that in vitro studies, clinically available anesthetics, such as intravenous anesthetics, local anesthetics and opioids have, more or less, possible antitumor potential against human malignant tumor cells. Although natural killer (NK) cells play an important role in tumor and metastasis surveillance, the reported effects of the anesthetics on the NK cell activity in human are controversial. Animal studies indicate that the neuroendocrine stress response to the surgery suppresses the immune function, particularly NK cell cytotoxicity, and increases the metastatic burden under inhalational anesthesia alone. Moreover, animal studies indicate that the addition of spinal block and optimum postoperative analgesia independently reduce the metastatic burden by blocking the stress response under inhalational anesthesia alone. Considering inconclusive results, especially in human, about evaluating the influence of anesthetics on malignant tumor, further studies in basic and clinical settings are required to study the effects of anesthetics on malignant tumor.