The conductivity of styrene-butadiene-styrene block copolymers containing different amounts of extraconductive carbon black (CB) was investigated as a function of the mold temperature. The composites exhibited reduced percolation thresholds (between 1.0 and 2.0 vol % CB). The dynamic mechanical analysis characterization revealed that the glass-rubber-transition temperatures of both segments were not affected by the CB addition, although the damping of the polybutadiene phase displayed a progressive drop with an increase in the CB concentration. The normalized curves of tan delta/tan delta(max) (where tan delta represents the value of the loss tangent at any measurement temperature and tan delta(max) represents the loss tangent peak value at the corresponding temperature T-max) versus T/T-max (where T is the temperature and T-max is the maximum temperature), corresponding to both polystyrene and polybutadiene phases as well as the activation energy related to the glass-rubber-transition process, did not present any significant change with the addition of CB. The dielectric analysis revealed the presence of two relaxation peaks in the composite containing 1.5 vol % CB, the magnitude of which was strongly influenced by the frequency, being attributed to inter-facial Maxwell-Wagner-Sillars relaxations caused by the presence of different interfaces in the composite. The mechanical properties were not affected by the presence of CB at concentrations of up to 2.5 Vol %. (C) 2003 Wiley Periodicals, Inc.