0-3 piezoelectric ceramic PMN/conductive carbon black(CB)/epoxy resin(EP) composites were prepared by resin casting method. The electric and damping properties of PMN/CB/EP composites were detected. The volume resistivity of the composites decreases with the addition of conductive carbon black, and the composites experience transition from insulator to semiconductor when the CB content is 6% weight of the resin in the composites. Damping loss factor-temperature curves scanned by DMA showed that the peak value of damping loss factor(tanmax), the loss factor area(TA) and the damping temperature range(T) of the composites increase and reach to maximum values when CB content is 6% weight of EP resin, then drop a little with CB contents further increasing. When CB was just at threshold content 6% of epoxy weight the composite converts from insulator to semiconductor with the volume resistivity being about 108 Ωm and piezo-damping mechanism plays efficiently.