olyethylene/montmorillonite (LDPE/MMT) nano-composites are prepared by melting intercalation process. The characteristics of electrical breakdown and partial discharge (PD) of the nano-composites are investigated. The test results indicate that electrical breakdown strength of LDPE/MMT is obviously higher than that of LDPE, up to 1.35~1.70 times at the test temperature of 333~363K, especially. The results of PD test indicate that under the same test condition both the amplitude and numbers of PD are smaller than pure PE.