Carbon-doping oxide materials (SiCOH films) with k of 2.62 are prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) from the mixture of decamethylcyclopentasioxane (D5) and oxygen (O2). This paper investigates the effect of O2-doping on bonding configuration, dielectric property and leakage current of the SiCOH low dielectric constant films. The results show that the leakage current can be reduced obviously on the premise that dielectric constant k is kept at a lower value by small O2-doping amount. For the SiCOH film deposited under O2 flow of 3 cm3/min, the dielectric constant k as low as 2.62 and leakage current of 8.2×10-9 A/cm2 can be obtained.