In the present study, fiber-matrix compatibility in an all-oxide ceramic composite is examined. Reaction-bonding aluminum oxide is used as porous matrix to ensure weak interfaces with fibers. Matrix cracks have been deflected around the interface for sintering temperatures up to 1300 degrees C, due to the effectiveness of porous matrix in enabling damage tolerance. Above 1300 degrees C, densification of the matrix resulted in brittle fracture of the samples, with matrix cracks going through the fibers. Observation of fracture surfaces confirmed the fiber pull-out phenomenon up to processing temperatures of 1300 degrees C. The well-known He and Hutchinson criteria for crack deflection was used to predict debonding behavior at the fiber-matrix interface as a function of matrix porosity. Furthermore, evaluation of the microstructure evolution of Nextel (TM) 610 alumina fibers showed a pronounced grain coarsening at sintering temperatures above 1300 degrees C. Changes in crack deflection behavior and fiber microstructure of a composite sample aged for 100h are also presented.