Polyethylene separator is irradiated by gamma ray to investigate the effect on electrochemical and thermal properties of polyethylene separators. Applied irradiation dose was 50, 100, 150 and 200kGy. It is observed that the melt integrity temperature is increased as the higher dose of irradiation is applied. In case of non-irradiated PE separator, shut-down temperature is about 133°C and melt integrity temperature is 146°C. On the other hand, the separator with irradiation dose of 200kGy, shut-down temperature is about 136°C and melt integrity temperature is about 166°C. Thermal shrinkage test is performed at 150 and 120°C for 1h each. It is observed that the irradiated separator has better thermal shrinkage resistance than the non-irradiated one because of the cross-link of polyethylene formed by gamma ray irradiation. Therefore, it can be concluded that the cross-link of polyethylene formed by gamma ray irradiation is strongly effective against thermal shrinkage. The electrochemical test is performed at high rate using the irradiated separator and the non-irradiated one to investigate any trade-off. The high rate discharge characteristic of the irradiated separator is better than that of the non-irradiated one. FTIR spectral analysis of the irradiated and non-irradiated separators is performed and ionic conductivity was measured to understand the reason.