It is significant to coat the surface of carbon fiber to improve its oxidation resistance, especially when it is used to prepare metal-matrix composites. In this paper, polytitanocarbosilane (PTC) was used as the precursor, carbon fiber as the original fiber, and Tyranno/C composite fiber was prepared by sintering at 1300 degreesC, in an inert atmosphere. A dynamics model for oxidation of the composite fiber at high temperature was established and the effects of coat thickness and crystalline form on oxidation resistance were studied. (C) 2003 Elsevier B.V. All rights reserved.