To provide a process for producing a reliable substrate in good yield, by suppressing bleeding of boric acid from a green sheet comprising a powder of borosilicate glass to improve printability of a conductive pattern thereby to prevent disconnection.A process for producing a substrate which comprises firing a green sheet comprising a powder of borosilicate glass, wherein the powder is one prepared by holding borosilicate glass before pulverization, at a temperature higher by at least 30° C. than the glass transition temperature and lower by at most 50° C. than the softening point of the borosilicate glass for at least 3 hours in the atmosphere, followed by pulverization.