The composition of fiber-matrix boundaries and the fractography of fracture surfaces in Nicalon/Sic composites have been analyzed by means of Electron Microprobe and Scanning Eletron Microscope (SEM) . The analysis shows that the creep failure of Nicalon/Sic composites is a completed and no-sudden brittle fracture process. Also, fiber-matrix bond strength has been semi-quantitatively evaluated by using indentation methods, and so the fiber pull-oot mechanism for increasing fracture toughness has been presented