6FDA-ODA polyimide was sulfonated with concentrated sulfuric acid at room temperature in order to convert the polymer into proton-conducting polymer. The sulfonation process was supervised with UV-vis. The results indicated that the reaction carried out quickly and was agreement with the analysis of resulted polymer. The sulfonation degree can be controlled by reaction time. The structure of the resulted polyelectrolytes were analyzed and confirmed by NMR, FT-IR. There are two weight-loss steps at 300 and 500 degrees C in TG curves, which correspond to the presence of two degradation processes for -SO3H and polymer backbone. It indicated that the sulfonated polyimide had good thermo stability. The solubility of sulfonated polymer are also discussed.