The present invention relates to an isolated peptide, an anti-cancer medicinal composition including the same and a method of specifically reducing or inhibiting activities of cancer cells using the same. The isolated peptide including a TAT basic domain conjugated to a GABARAPL2 H2 domain can specifically reduce or inhibit an activity of cancer cells, thereby being applied to the anti-cancer medicinal composition and the method of specifically reducing or inhibiting activities of cancer cells using the same.