Cantharidin (CTD) is a bioactive ingredient isolated from Cantharis vesicatoria (blister beetles), which has potential therapeutic value as an anticancer agent. Magnesium Demethylcantharidate (MDC) is a recently developed derivative of Cantharidin (CTD), and previous studies have illustrated its excellent anticancer activity on HCC cells.However, the effect and mechanism of MDC remains unclear and need to be further studied. In particular, whether MDC can cause ER stress in HCC is still unknown. In this study, we demonstrated that endoplasmic reticulum stress (ERS)-related proteins were changed in SMMC-7721 and Bel-7402 cells after being exposed to MDC. Moreover, we found that MDC could significantly inhibit the growth of xenograft tumor in nude mice. In summary, we confirmed that MDC could induce ERS in HCC cells and thus induce apoptosis.