Natural product extracts are a rich source of small molecules that display antitumor activity. Cantharidin, in the form of the dried body of the Chinese blister beetles: Mylabris phalerata or M. cichorii, displays antitumor activity and induces apoptosis in many types of tumor cells. Cantharidin has been used as an anticancer agent by the Chinese for the treatment of hepatoma and oesophageal carcinoma for a long time. Although cantharidin is a natural toxin that possesses potent anti-tumor properties, its clinical application is limited due to severe side-effects and highly toxic nature. Therefore, some modified cantharidin analogues are synthesized chemically in order to achieve a comparable antitumour property to the mother compound but simultaneously produce a less toxic effect on non-cancer cells. In recent years, based on the structure of cantharidin, there has been intense interest in developing potent and selective inhibitors of PP1 and PP2A on tumour cells. Though numerous analogues of cantharidin have been synthesized and researched with tumour cell lines, there is little success on clinical application because of the potential toxicity of cantharidin derivates. The focus of this review is to describe how cantharidin and cantharidin derivates participate in antitumour processes in tumour cells, and discuss the molecular mechanisms of cantharidin and cantharidin derivates on tumour cells.