A series of Nicalon SiC fibers (202) coated by CVD with C and SiC were analysed by Secondary Ion Mass Spectrometry (SIMS). Results (i) give the composition of the material, (ii) show its heterogeneity of composition, and (iii) demonstrate the limit of application of the method for the fibers analyses. SIMS and Electron Energy Loss Spectroscopy (EELS) analyses of one coated fiber segment were done. When elements are detected by both techniques, reasonable agreement is observed between the results. SiC - CVD deposits are not uniform: they are rich in carbon close to the fiber and tend towards stoechiometry after a few microns. The coated fibers are rich in oxygen and in free carbon. Analyses of a glass-ceramic matrix/ Nicalon SiC fiber (202) composite were performed using SIMS, EELS and Energy Dispersive X-Ray Spectroscopy (EDX).