A study on the correlation between electrical percolation and viscoelastic percolation for carbon black (CB) and carbon fiber (CF) filled high-density polyethylene (HDPE) conductive composites was carried out through an examination of the filler concentration (phi) dependence of the volume resistivity (rho) and dynamic viscoelastic functions. For CB/HDPE composites, when phi was higher than the modulus percolation threshold (phi(G) similar to 15 vol %), the dynamic storage modulus (G') reached a plateau at low frequencies. The relationship between rho and the normalized dynamic storage modulus (G'(c)/G'(p), where G'(c) and G'(p) are the dynamic storage moduli of the composites and the polymer matrix, respectively) was studied. When phi approached a critical value (phi(r)), a characteristic change in G'(c)/G'(p) appeared. The critical value (G'(c)/G'(p)c) was 9.80, and the P corresponding phi(r) value was 10 vol %. There also existed a phi dependence of the dynamic loss tangent (tan delta) and a peak in a plot of tan delta versus the frequency when phi approached a loss-angle percolation (phi(delta) = 9 vol %). With parameter K substituted for A, a modified Kerner-Nielson equation was obtained and used to analyze the formation of the network structure. The viscoelastic percolation for CB/HDPE composites could be verified on the basis of the modified equation, whereas no similar percolation was found for CF/HDPE composites. (C) 2004 Wiley Periodicals, Inc.