A new modeling approach to subcritical crack propagation ( static fatigue) in ceramics is introduced and applied to the case of ceramic fibers. This approach relies on classical fracture mechanics, in which the zone near the crack's tip is modified by the environment (particularly through oxidation). Chemical reactions and diffusion are introduced naturally, which makes the model highly dependent on the environmental conditions, such as partial oxygen pressure. In some cases, the result comes down to the widely-used Paris-like subcritical crack propagation law. For the general case, a two-parameter model calibrated and validated up to 1,000 C for Hi-Nicalon fibers is presented.