Abstract: Silica-alumina fibers having good mechanical strength and heat resistance are produced by mixing a polyaluminoxane which comprises repeating units of the formula: ##STR1## in which X is an alkyl group, an alkoxy group or a hydroxy group, a silicon-containing compound in an amount of not larger than 40% by weight in terms of silica based on the weight of silica-alumina fibers to be produced, and an aliphatic carboxylic acid having 2 to 14 carbon atoms in an alkyl group in an amount of 0.03 to 0.4 mole per one gram atom of aluminum to obtain a spinning liquid, spinning the spinning liquid under a condition that a content of nonvolatile materials in the solution is maintained at least 97% by weight to form precursor fibers, and calcining the precursor fibers.