Disclosed is an external preparation composition having good transdermal absorbability. An external preparation composition having excellent transdermal absorbability can be produced by dissolving a medicinal substance or a salt thereof in a fatty acid-based ionic liquid to form a composite ionic composition of the medicinal substance. The external preparation composition can be used as a liquid preparation, an ointment, a cream, a plaster or the like, and enables to provide a preparation having excellent transdermal absorbability.
