An ionic liquid, 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMI-FSI), has been applied to an electrolyte for electric double layer capacitors (EDLCs). The electrolyte exhibited high ionic conductivity comparable to that of a conventional organic electrolyte. EDLC prepared with EMI-FSI showed excellent rate capability although the electrolyte is a neat ionic liquid; this performance was observed irrespective of the presence of a binder in an activated carbon-based electrode. The self-discharge was suppressed by using EMI-FSI. A cycling durability test showed that the cell with EMI-FSI kept over 90% of the initial capacitance even after 10,000 cycles.