Room temperature ionic liquids are composed of only ions and have been widely applied in various fields. DNA double helix, which is a genetic material, has been expected its application in chiral material science and electrochemistry as a natural chiral supramolecule. However, it is difficult to use DNA double helix as a material due to its insolubility in organic solvents. Herein, we studied the construction of the double helical DNA and the expression of its functions in ionic liquids. Hydrophilic ionic liquids containing water can dissolve DNA, and C-form DNA double helix, whose structure is different from that in water, was formed with increase the proportion of the ionic liquids. The water-insoluble porphyrin, THPP, can also interact with DNA double helix in the ionic liquid solution, and its induced CD signals by chiral DNA double helix indicated that THPP bound to DNA with different modes depending on the structure of ionic liquids. Construction of DNA double helix in ionic liquids, which are functional solvent themselves, enables the utilization of DNA as a functional material.