The influences of functional polysiloxanes bearing epoxy or amino groups on the thermooxidative stabilization process of the PAN precursor fibers were studied. Structural changes were investigated by FT-IR spectroscopy. It was found that formation of the conjugated ladder structure in the precursor fiber was promoted by the functional polysiloxanes. Meanwhile heat releasing in the thermooxidative stabilization process was depressed. It seems that the coatings of the functional polysiloxanes on the fibers retarded oxygen diffusion into the PAN precursor fibers. The functional polysiloxanes did not affect carbonization in an inert atmosphere following the thermooxidative stabilization process. (C) 2004 Kluwer Academic Publishers.