Silicon-based films have gained much interest as protective coatings for transparent polymeric materials. In this study, SiOC(-H) thin films were deposited on polycarbonate (PC) or Si substrates from trimethylsilane (TrMS) gas diluted with He gas by atmospheric pressure plasma enhanced CVD (AP-PECVD) method with varying substrate temperature, and transparency and hardness of the films were investigated. The films exhibited a good optical transparency with an optical transmittance of about 90% irrespective of the substrate temperature, and the hardness increased from 0.6 to 1.3 GPa as the substrate temperature increased from 60 to 140°C. The results are discussed in terms of chemical structural changes in the films according to the substrate temperature. © 2011 Materials Research Society.