This paper investigates the effect of Si-OH group oil dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane electron cyclotron resonance plasma. The results show that the increasing of Si-OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and stronger dielectric dispersion. Due to the strong polarization of Si-OH group, it leads to the increase of k value of the SiCOH films. The decreasing of leakage Current at high Si-OH content is due to the low connecting probability p of networks because the networks break at the terminal Si-OH groups. At the case of high ionization degree of precursor, more Si-OH groups break and form Si-O-Si linkages by condensation chemistry occurring between proximal Si-OH groups. As a result, the k value of SiCOH films call be further reduced, (c) 2005 Elsevier B.V. All rights reserved.