Nanocomposite γ-Al2O3/PE separators for lithium battery were prepared by radiation. Nanocomposite γ-Al2O3/PE separators showed electrolyte uptake of 157% and ionic conductivity of 1.3 mS/cm. Nanocomposite γ-Al2O3/PE separators showed high heat-resistance property at 150 °C. Coin cell assembled with nanocomposite γ-Al2O3/PE separators showed excellent electrical performance.