In this study, a hydrophobic silica aerogel was synthesized via one-step surface modification and polymer composite films based on a polyurethane (PU) matrix were prepared by doping with silica aerogel powder (at 2%, 3%, 5%, and 7% by weight = w/w%). The structural, thermal, morphological, and surface properties of the silica aerogel and PU composite films containing aerogel were investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), scanning electron microscopy, and tensiometry. The dielectric properties of the silica aerogel and PU composite films containing the aerogel were determined over a temperature range of 293-423 K and a frequency range of 1-10(6) Hz. The contact angle of the silica aerogel was 10(6). Moreover, the PU composite film with 7% aerogel had the highest contact angle (theta = 105 degrees) among the composite samples, which was similar to contact angle of the silica aerogel. The dielectric constants and dielectric losses decreased with the frequency for all of the samples, whereas they increased with the temperature. The polarization regions and relaxation times were determined for all of the samples using the Cole Cole equation. The glass-transition temperatures (T-g) were determined for the silica aerogel and PU composite films containing aerogel by dielectric spectroscopy and compared with the DSC results. The dielectric constants were lower for the PU composite films than the PU film. The dielectric constant for the PU composite film doped with 2% silica aerogel was 2.9 at 10 MHz. Thus, the PU composite with a low dielectric constant and dielectric loss factor (tan delta) could be regarded as a potential dielectric constant candidate, with possible applications as a dielectric material in the microelectronics industry.