A nanocomposite including: a sulfonated polysulfone and a nonmodified clay dispersed in the sulfonated polysulfone, the nonmodified clay having a layered structure, and the nonmodified clay being intercalated with the sulfonated polysulfone, or the layers of the layered structure being exfoliated, a nanocomposite electrolyte membrane and a fuel cell using the same. In the nanocomposite, a nanoscale amount of the nonmodified clay, which has a layered structure, is dispersed in sulfonated polysulfone having excellent ionic conductivity. Thus, the nanocomposite has excellent ionic conductivity and mechanical properties. The nanocomposite electrolyte membrane formed using this nanocomposite has an improved ability to suppress permeation of polar organic fuels, such as methanol, while maintaining appropriate ionic conductivity. In addition, the fuel cell with the nanocomposite electrolyte membrane can effectively prevent crossover of methanol used as a fuel, thereby providing improved working efficiency and an extended lifespan.