A series of carbon black containing interpenetrating polymer networks (IPNs) based on unsaturated polyester/epoxy (weight ratios 10/90, 20/80, 30/70) were developed. Scanning electronic microscopy exhibits that the compatibility was decreased and the morphology seemed to become less rigid as the content of unsaturated polyester increased in lPNs. The results also indicate that flame retardants were uniformly distributed in the IPN matrices. It is found that the heat resistance, damping, and mechanical properties were all improved simultaneously by adding the plate-shaped carbon black flame retardants to the unsaturated polyester/epoxy IPNs.