Composite sol with spinnability was prepared from an aqueous solution using polyvinyl butyral (PVB), Al (NO3)3·9H2O (AN) and tetraethylorthosilicate (TEOS) via non-hydrolytic sol-gel method. The mullite fibers with good flexibility were also obtained. The viscosity of composite sol increased with the increasing PVB content, water-bathing temperature and aging time. FTIR spectroscopy of composite gel showed a new absorption peak due to the C=O group, which implied the presence of new reaction product. It could be explained by the reaction among PVB, AN and TEOS.