Arsenic compounds are natural substances that have been used medically for more than 2,400 years in China. Since 1990s, Chinese physicians have began to use arsenic trioxide in treating the patients with acute promyelocytic leukemia (APL), and the results showed that arsenic trioxide was effective on APL patients. Further study of arsenic trioxide demonstrated that arsenic trioxide was safe and effective not only on patients with leukemia, but also on patients with many other kinds of malignant cancers. Arsenic trioxide exerted its anti-cancer effects mainly by inhibiting the cell growth and angiogenesis, inducing the cell partial cytodifferentiation and apoptosis, etc. In addition, this review looked forward to the prospect of application of gene chip, a newly developed and powerful technology in analysis of gene expression profile, in elucidation of the mechanism of arsenic trioxide on tumor.