The present invention relates to an anticancer adjuvant containing, as an active ingredient, protopanaxadiol (PPD) or a compound-K, which are types of panaxadiol ginsenoside compounds, and a pharmaceutical composition for treating cancer containing the anticancer adjuvant and an anticancer agent having mitochondria-mediated anticancer activity. The anticancer adjuvant containing the PPD or compound-K provided in the present invention as an active ingredient damages mitochondria in cancer cells, thereby aiding mitochondria-mediated anticancer activity, and thus can be widely used in safer treatment or alleviation of cancer using anticancer agents that exhibit mitochondria-mediated anticancer activity.