PURPOSE: To obtain a board capable of excellenty cutting off ultraviolet rays, by making fluorescent brightener adhere to glass fiber base material for printed wiring board.

CONSTITUTION: Fluorescent brightener is made to adhere to the surface of a constituted glass fiber of fiber sheet of woven fabric composed of glass fiber, unwoven fabric, paper etc. As the fluorescent brightener, the following are used; bis(triazinyl-amino)stilbenedisulfonic acid, coumarin, pyrazoline, naphthalimide, bisbenzoxazolyl and bisstyrylbiphenyl. A printed wiring board formed by laminating a plurality of prepregs manufactured by using the above base material converts ultraviolet rays projected from one surface to fluorescence, and can prevent the ultraviolet rays from reaching the other surface.