Lyotropic liquid crystals (LLCs) have been attracting attention as new transdermal drug delivery carriers because of their high stability compared with that of other liquid carriers, such as emulsions, micelles, and liposomes.However, the transdermal delivery performance of LLCs is not satisfactory because their high viscosity often reduces the permeation rate of the drugs.In the present study, to improve the performance of LLCs as a drug delivery carrier, we have developed an ionic liquid crystal (ILC) formulation by adding an ionic liquid (IL) component as a mesogen, which can enhance transdermal permeation.A biocompatible ionic liquid IL [Cho][Ole], composed of choline and oleic acid, was synthesized for pharmaceutical applications.The ILC formulations loaded with 1 wt% of favipiravir (FAV), which had potential as a therapeutic agent for coronavirus infections, showed excellent stability.In vitro drug permeation experiments using mouse skin indicated that the ILCs enhanced the permeability of FAV.In particular, FAV-ILC-70 (IL [Cho][Ole] : water = 7 : 3 (w/w)), which has a gyroid structure, significantly improved the transdermal delivery of FAV by fluidizing the stratum corneum lipids.These results suggest that liquid crystalline formulations with biocompatible ILs are promising new transdermal drug delivery carriers.