Camphorsulfonic acid (CSA)-doped polyaniline (PANI) and thermally reduced graphene (TRGO) composite polymer film with high thermoelectric (TE) properties were fabricated. We developed a modified Hummers method with an additional ultrasonic disruption technique to obtain well-isolated TRGO powder and well-dispersed PANI–CSA–TRGO composite polymer. Transmission electron microscope (TEM) observation, electron energy-loss spectroscopy, and Fourier transform infrared spectroscopy analyses revealed that the ultrasonic disruption process produced a well-isolated state of graphene oxide, and this state remained after a thermal reduction process. The dispersed TRGO powder was added to CSA-doped PANI composite polymer to improve its electrical conductivity (EC) properties. Addition of the well-isolated TRGO powder with high crystallinity resulted in remarkable improvement in EC without any degradation of the Seebeck coefficient (SC), which is representative of TE properties. The highest SC and EC values obtained in this study were 24 μV K−1 and 3677 S cm−1, respectively, which were observed for the 30 wt% TRGO-added PANI–CSA composite film, and the resulting power factor reached 214 μW mK−2. Well-isolated graphene with high crystallinity was fabricated using an additional ultrasonic disruption process, and well-dispersed polymer/graphene composite was also fabricated using the same sonication process. This optimized sonication process is simple but effective for improving TE properties of the composite.