Carbon elimination from EB-cured PCS fibers by H-2-treatment and the thermal stability of resultant SiC fibers were examined through TG, chemical analysis, AES analysis, XRD analysis, resistivity measurements, SEM observation and tensile tests. The C/Si mole ratio from 1.50 to 1.05 could be achieved by H-2-heat treatment at tgreater than or equal to4 h and T=773-1173 K. There was no difference in XRD patterns, fiber morphology and tensile strength of the fibers in the as-H-2-treated state. H-2-treatment at higher temperature caused the reduction in residue and the increase in resistivity of the fibers. An oxygen-rich layer was formed on the fiber surface after H-2-treatment, resulting in the mass loss, the coarsening of beta-SiC grains and a marked degradation of fiber strength after exposure to higher temperature. Prevention of oxygen uptake after H-2-treatment is essential to improve the thermal stability of SiC fibers. (C) 2004 Kluwer Academic Publishers.