Propylene carbonate (PC) is a common organic solvent used in lithium batteries due to its high dielectric constant and high chemical stability with lithium. However, the conductivity of PC-based electrolytes is about two orders of magnitude lower than those of aqueous electrolytes. To increase the conductivity of PC-based electrolytes, a co-solvent, ethylene carbonate (EC), is added to the electrolyte to form a mixed solvent. In this research, the conductivity of electrolytes as a function of lithium perchlorate (LiClO4) salt concentration and EC/PC molar ratio have been studied. The highest conductivity, 1.4 x 10(-2) S cm(-1), occurs when the salt concentration is about 1 mol L-1 and the EC/PC molar ratio is about one. To understand the composition dependence of the conductivity, the interaction between Li+ and EC molecule has been studied using Raman spectroscopy. These results showed that the solvation number of Li+ increases with increasing the EC/PC molar ratio at constant LiClO4 concentration and the solvation number of Li+ decreases with increasing the LiClO4 concentration at constant EC/PC molar ratio.