The present invention relates to an anticancer supplement containing loperamide as an active ingredient. More specifically, a proteasome inhibitor alone cannot exhibit an anticancer effect on solid cancers and some blood cancers, but when the proteasome inhibitor and loperamide are co-administered or a composition containing the proteasome inhibitor and loperamide is provided, cancer cell death by the proteasome inhibitor can be effectively induced, thereby exhibiting an improved anticancer effect, and enhancing anticancer effects on solid cancers and blood cancers while reducing side effects caused by a high-concentration of the proteasome inhibitor. Therefore, the composition containing the proteasome inhibitor and loperamide as active ingredients, according to the present invention, can be useful for preventing or treating cancer, and loperamide can be provided as an anticancer supplement when the proteasome inhibitor is used to treat cancer.