The electrical breakdown is investigated in high-density polyethylene/graphite nanosheets (HDPE/GNs) conductive composites. A sample suffers electrical breakdown when the applied field exceeds the critical electrical breakdown field below which the sample reaches a stable state. It is found that the ratio of the critical electrical breakdown resistance to the linear resistance assumes a fixed value Y, which is found to be about 1.30 in HDPE/GNs conductive composites. The value Y is independent of GNs' content, sample size, breakdown cycle, but depends on the property of GNs. The critical breakdown field E-b scales with the resistance R-0 as E-b similar to R-0(yb) with the exponent y(b) = 0.46 +/- 0.02, which is close to the value predicted in mean-field theory but higher than the value given by the singly connected bonds networks. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 576-582, 2009