Abstract: A glow plug for diesel engines in which a ceramic heater is supported, with the one end thereof cantilevered toward the outside, by the tip of a hollow holder; the ceramic heater is composed of a U-shaped heating portion and a pair of leads extending backwards from both ends of the U-shaped heating portion, both being formed integrally by an electrically conductive sintered sialon, which is formed by adding a small amount of Al.sub.2 O.sub.3 to a raw meal containing Si.sub.3 N.sub.4 as a principal ingredient, a small amount of AlN polytype and no greater than 5 wt. % of Y.sub.2 O.sub.3, and mixing the addition product with 23-70 vol.