The present invention relates to a pharmaceutical composition for preventing or treating familial hypercholesterolemia, which comprises a Morus alba extract or a compound isolated from the Morus alba extract as an active ingredient. More specifically, the Morus alba extract or the compound isolated from the Morus alba extract of the present invention exhibits an effect of inhibiting the overexpression of proprotein convertase subtilisin/kexin type 9 (PCSK9), and thus can be applied to various fields such as pharmaceutical industry or health functional food for preventing, ameliorating or treating familial hypercholesterolemia caused by overexpression of PCSK9.