NOVELTY - A linear polyethyleneimine structure-containing polymer is added to aqueous medium in presence of ice. Alkoxysilane is added to aqueous medium to form disc-shaped composite nanofibers comprising silica-coated aggregate. The obtained composite nanofibers are mixed with hydrolyzable metal compound, and metal oxide is deposited on fiber surface. Nanofibers are baked, and polymer in composite nanofibers is removed to obtain silica nanofibers. Silica nanofibers are combined with metal oxide nanocrystals to obtain silica nanofiber/metal oxide nanocrystal composite.    USE - Manufacture of silica nanofiber/metal oxide nanocrystal composite used for fluorescent substance (claimed). Uses include but are not limited to photocatalyst, solar cell, deodorization material, fluorescence material, dielectric material, magnetic material, stimulus response material, sensor, insulating material and catalyst material.    ADVANTAGE - The method efficiently and economically provides silica nanofiber/metal oxide nanocrystal composite having high durability by simple method.    DETAILED DESCRIPTION - A polymer having linear polyethyleneimine structure, is added to an aqueous medium in presence of ice. Alkoxysilane is added to the resultant aqueous medium to form disc-shaped composite nanofibers comprising silica-coated aggregate, and the composite nanofibers are capable of spontaneously forming network-type disc-shaped structure. The obtained disc-shaped composite nanofibers are mixed with hydrolyzable metal compound in aqueous medium, and metal oxide is deposited on the fiber surface. The obtained nanofibers are baked at 400-1250 degrees C, and polymer in the composite nanofibers is removed to obtain silica nanofibers. The obtained silica nanofibers are combined with metal oxide nanocrystals to obtain silica nanofiber/metal oxide nanocrystal composite. INDEPENDENT CLAIMS are included for the following:    (1) silica nanofiber/metal oxide nanocrystal composite, which has thickness of 5-500 nm and diameter of 5-20 mu m; and    (2) fluorescent substance, which is obtained by exciting silica nanofiber/metal oxides nanocrystals under ultraviolet irradiation.