PURPOSE: To stably and efficiently obtain a fibrous inorganic product, by subjecting a raw material containing a metal alkoxide and a specific organic compound to hydrolysis and polymerization reaction in controlled water content and reaction temperature and cooling the resultant sol to a prescribed low temperature and spinning the cooled sol and then burning spun material.

CONSTITUTION: A raw material containing a metal alkoxide expressed by formula I and organometal compound expressed by formula II [M and M' are Si, B, Ti, Zr or Al; R, R' and R" are CH3, C2H5, C3H7 or C4H9; n is 3 or 4; m is 1-(n-1)] is prepared. Then water of amount expressed by formula III [P(H2O) is molar ratio of added water content to mole number of water required to theoretically and completely carry out hydrolysis and polymerization reaction], catalyst and as necessary solvent are added to the above-mentioned raw material. Then the hydrolysis and polymerization reaction of the above- mentioned raw material is carried out at 10-80°C and then formed sol solution is cooled and spun while keeping to 0--50°C and the resultant fiber is heated and burned to provide the fibrous inorganic product.