Ionic liquids (ILs) containing ester group have been synthesized and the physical and electrochemical characteristics have been investigated. The ILs showed high thermal stabilities (over 300 ^oC) and low meting temperature around -42 ^oC. These ILs exhibit ionic conductivity as high as 3 mScm^-1 at 60 ^oC. Most importantly, the imidazolium and piperidinium-based ILs showed very wide electrochemical windows of ~ 5.5 V. Due to their excellent physical and electrochemical properties, these ILs may be promising candidates to the electrolytes in the secondary batteries and the dye-sensitized solar cell system.