The effect of firing on the development of strength of china with maturing range of a series of glaze that gave no defect on firing was observed in an electrical furnace and oil-fired kiln. The body formular is as follows (equation omitted), and it was applied to a selected china body. Porcelain glaze formular is in the following. (equation omitted) The result obtained is sumarized as follows : (1) It was found that the strength of porcelain increases when the A1$_2$O$_3$ moles of the glaze increses, and the strength of porcelain decreases when the SiO$_2$ moles of glaze decreases at 3.9-5.9 moles, and increases again when the SiO$_2$ moles increases at 5.9-7.9 notes. (2) It was found the most safe glaze is No. 25 glaze.