Polymeric fibers were produced from a polyaluminocarbosilane obtained by reacting polycarbosilane and an aluminum alkoxide modified with a p-ceto ester. The pre-ceramic fibers were converted into amorphous Si-Al-0-N ceramic fibers after a pyrolysis process under flowing ammonia at 1000°C. "Si and "AI magic-angle spinning nuclear magnetic resonance investigations were performed to characterize the conversion process of the polymeric precursor fibers into the ceramic product. However, because of the amount of matter required for the MAS-NMR experiments, the heat treatment applied for fibers was done on powders assuming identical evolution for both materials. Tensile strength was measured at various stages of the pyrolysis process and related to the corresponding structural evolution.