SiCOH films were deposited with plasma-enhanced chemical vapor deposition using vinyltrimethylsilane (VTMS) as a precursor and CO2 as an oxidant. The properties of the films were compared with those films deposited with VTMS and O2. As-deposited films and the films annealed at 360 °C have been characterized. The growth rate decreased with increasing substrate temperature and increased with increasing CO2/precursor ratio and plasma power. The dielectric constant was inversely proportional to the relative carbon content and the films deposited with CO2 had a higher carbon content than those deposited with O2. It was confirmed that CO2 was more effective to increase the carbon content. The refractive index of the as-deposited films was about 1.48–1.49 and decreased to 1.46 after annealing. The reduction of the refractive index was due to the lower density and increased porosity of the film. After annealing, the SiCOH films showed a low dielectric constant of 1.9 at optimum condition.