Commercial polysiloxanes filled with alumina nanoparticles and AlN and Si3N4 micropowders have been used for the preparation of beta-SiAlON in nitrogen, at 1450 degrees-1550 degrees C. SiAlON was preceded by intermediate alumino-silicate phases like mullite and sillimanite. Although reduction and nitridation to beta-SiAlON finally occurred, the SiAlON yield at high temperatures was lowered by corundum contaminations. The yield was also possibly affected by phase separation in the SiOC glass residue derived from silicones. A composition refinement reduced contamination and provided a promising route for SiAlON from filled preceramic polymers.