Objective To elaborate the physiological functions of orexin and the correlation between leptin and malignant tumor, in addition to look forward its application prospect in tumor. Methods We reviewed and researched the domestic and foreign published literature about the physiological function of orexin, and the relationship between leptin and malignant tumor. Results Orexin can not only be involved in the regulation of energy metabolism, feeding behavior, but also play a very important role in the sleep wake cycle, stress, drug addiction and relapse, insulin secretion, gastric acid secretion, and many studies have confrmed that orexin can affect the appetite of patients with malignant tumor and promote the apoptosis of cancer cells. Conclusions Orexin has the application prospect in drug discovery for treating diabetes, drug addiction and narcolepsy, improving the poor quality of appetite in patients with malignant tumor and promoting the apoptosis of malignant tumor cells.