A series of BaTiO3 fiber and nanopowder unfilled and filled interpenetrating polymer networks (IPNs) composed of polyurethane (PU) and unsaturated polyester resin (UP) are prepared by simultaneous polymerization process. The effect of PU/UP component ratios, the types and amounts of BaTiO3 filled, the polarization treatment to filled IPNs, on the damping properties are investigated by dynamic mechanical thermal analyzer (DMTA). The morphology and microstructures of unfilled and filled IPNs are examined by transmission electron microscope (TEM). The dielectric loss and dielectric constant at different temperatures are studied by AC impedance analyzer. Moreover, the relationship between damping and dielectric properties is discussed in terms of dielectric constant and dielectric loss measured. The results show that the PU/UP component ratios in IPNs, the types of filler, and the amount of nanopowder added all affect the damping behaviors and degree of phase separation of unfilled and filled IPNs. Through polarization treatment, the filled IPNs exhibit synergistic action in systems caused by elastomeric damping mechanism, interfacial frictional damping mechanism and piezoelectric damping mechanisms. The maximum value of E" of filled IPNs with 70% BaTiO3 increase above 100 MPa and the temperature ranges of tan delta > 0.3 is higher than 100 degrees C compared with unfilled IPNs. Moreover, the maximum value of E" and the temperature ranges of tan delta > 0.3 increases dramatically after polarizing process. The dielectric properties and its relation with damping properties studies reveal that the temperature ranges exhibit excellent consistency of maximum dielectric loss and dielectric constant with damping loss factor. (c) 2005 Springer Science + Business Media, Inc.