Sixteen new guanidinium salts based on small cations and TFSI- anion were prepared and characterized. Physical and electrochemical properties of these products, including melting point, thermal stability, viscosity, conductivity and electrochemical window were investigated. Reducing symmetry of cations can reduce the melting points, and 12 products are liquids at room temperature. The viscosities of cg22TFSI, cg12TFSI and cg13TFSI were 45, 46 and 52 mPa s at 25 degrees C, respectively. Electrochemical and thermal stabilities of these ILs permitted them to become promising electrolytes used in electrochemical devices. (C) 2008 Elsevier Ltd. All rights reserved.