This paper reports on the structural, thermal, and dielectric properties of polypyrrole/fullerene C-60 nanocomposites synthesized by a interfacial polymerization method. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) analyses clearly indicated the existence of interactions between polypyrrole (PPy) and the fullerene C-60 nanoparticles. Thermal analyses indicated that the extrapolated onset degradation temperature (T-deg) of PPy increased with increasing doping level. Scanning electron microscopy (SEM) images showed that the fullerene C-60 changed the morphology of PPy. Dielectric analyses showed a temperature dependent dielectric relaxation behavior. The relaxation time of the nanocomposites with high doping levels tended to increase with increasing temperature. This behavior of the polypyrrole/fullerene C-60 nanocomposites indicated that they could be used as a high temperature ultrasonic transducer.