Abstract: A process for producing an alumina-based fiber, which involves mixing an aluminum compound represented by the general formula AIR.sub.1 R.sub.2 R.sub.3 (wherein R.sub.1 R.sub.2 and R.sub.3 are each an organic group or a halogen) with water in a molar ratio of ([H.sub.2 O]/[AIR.sub.1 R.sub.2 R.sub.3 ]) of 1.10 to 1.40 to produce a polyaluminoxane, mixing the polyaluminoxane with at least one silicon-containing compound in an amount such that desired alumina-based fiber has, after calcining, a silica content of up to 70%, spinning the resulting mixture of polyaluminoxane and silicon-containing compound under an atmosphere controlled at a temperature of above 28.degree. C. and a relative humidity of above 35% to obtain precursor fiber, and then calcinating the precursor fiber to obtain an alumina-based fiber.