The use of botulinum toxin type A in the lower face has increasingly popular. And treatment of the depressor anguli oris muscle(DAO) and the mentalis muscle(MT), particularly in combination with filler substances, produces a remarkable improvement in the lower aged face. The aim of this study was to demonstrate the topographical anatomy of the DAO, MT, and their related structures, thereby providing critical information for determining the safest and most effective site for BTX-A injections. The most effective injection sites of DAO and MT were suggested based on the new anatomical knowledge of the lower face.