Low-dielectric-constant SiOC(-H) films were deposited, with and without ultraviolet (UV) irradiation, on p-Si(100) substrates from dimethyldimethoxysilane (DMDMS) and oxygen precursors by using plasma enhanced chemical vapor deposition (PECVD). The DMDMS/O2 flow rate ratio was varied from 10 to 100% in order to investigate the variations in the electrical properties with different deposition parameters. The dielectric properties of the film were measured using a metalinsulator-semiconductor (MIS), Al/SiOC(-H)/p-Si(100), structure. We found that the maximum capacitance depended on the precursor flow rate ratio. The detailed electrical properties, such as the flat band voltage, the leakage current density, and the oxide charge density of the SiOC(-H) film, for various flow rate ratios are discussed. A dielectric constant as low as 2.1 was obtained for the as-deposited SiOC(-H) films with UV irradiation.