Deoxyribonucleic acid (DNA) was mixed with ionic liquids to give flexible films having high ionic conductivity. Four ionic liquids were synthesized and mixed with DNA. When ethylimidazolium tetrafluoroborate (EtImBF(4)) was mixed with DNA, a flexible film was obtained over a wide range of EtImBF(4) proportions. Ionic liquids having an imidazole ring showed good affinity with DNA. The ionic conduction of a DNA film containing 93.9 wt % EtImBF(4) was 5.05 x 10(-3) S cm-l at 50 degreesC. This is comparable to the conductivity of EtImBF(4) in the bulk (2.02 X 10(-2) S cm(-1)). The film has two glass transition temperatures and is therefore suggested to undergo microphase separation, which is effective in constructing continuous ion conducting paths. This hypothesis is supported by the observation that a DNA/EtImBF(4) (37.5 wt %) mixture has different conduction characteristics from other ionic liquid-rich films.;