A modification process of the synthetic quartz powder, which can make a quartz glass product hardly having bubbles at the time of fusing, is provided, along with a modification process of the synthetic quartz powder and a glass product using said modified quartz powder are provided, wherein the synthetic quartz powder is kept in helium atmosphere at least in the temperature falling process, when the amorphous synthetic quartz powder produced by the sol-gel method is carried out by heat treatment in a vacuum furnace at more than the degas temperature and less than the baking temperature, wherein the highest temperature in the helium atmosphere is preferably set to from more than 700° C. to less than 1400° C., and the helium atmosphere is kept to less than 400° C.