Vanadium compounds are promising anti-diabetic agents. Although BEOV was not able to succeed in phase II clinical trial, great progresses have been made in the past three decades on the discovery and development of anti-diabetic vanadium compounds. A vast of knowledge has been obtained on the molecular mechanisms of both the pharmacological and toxicological effects of vanadium complexes. It has been revealed that vanadium compounds exert insulin enhancement effects and cell protection via a multiple mechanism involving inhibition of PTP1B, activation of PPARs- AMPK signaling, regulation of unfolded protein responses (UPRs), and stimulation of antioxidant enzymes, while vanadium-induced oxidative stress and inflammatory response could primarily be attributed to vanadium toxicity. Based on the present results concerning the relationship between structures, biological activities and biochemical properties, the rationale for future design of anti-diabetic vanadium compounds has been discussed.