SiOx-DLC (diamond-like coating) films as candidates for protection coating of polymers were prepared by using a pulse-biased inductively coupled plasma chemical vapor deposition system with acetylene, tetramethylsilane and oxygen gasses. Effects of the gas composition and O-2 plasma pre-treatment on adhesion of the SiOx-DLC films were investigated. Adhesion strength of Si-DLC films (with 0% oxygen) was almost the same to that of undoped DLC films. By employing O-2-plasma pre-treatment, adhesion strength of the Si-DLC films was considerably improved, while that of the undoped DLC films was not The SiOx-DLC films with the carbon to oxygen (O/C) ratio of 0.15 showed adhesion strength as high as that of the Si-DLC films on the O-2-plasma pre-treated substrate. However, further improvement of adhesion strength of the SiOx-DLC was not realized by employing the O-2-plasma pre-treatment. On the other hand, the SiOx-DLC films showed favorable feature of high deposition rate and large optical band gap although higher O/C ratio (>0.15) brought about poor adhesion strength of the films. (C) 2011 Elsevier B.V. All rights reserved.