Ionic liquids allow millimeter-long single-walled carbon nanotubes to associate tightly, forming a free-standing sheet with superb mechanical and electrical properties. An actuator strip, fabricated by sandwiching an ionic-liquid-gel electrolyte layer with the nanotubes sheets obtained exhibits a large deformation in quick response (4 mm per 0.05 s) to low applied voltages, and a high durability upon 10 000 times continuous operations.