A Spark plug has a central electrode, an insulator provided exterior to the central electrode, a metallic shell provided exterior to the insulator in such a way that the central electrode protrudes from one end, a ground electrode coupled at one end to the metallic shell and which has the other end disposed to face the central electrode, and an igniting portion secured to either the central electrode or the ground electrode or both to form spark discharge gap g. The igniting portions are each composed of a chip made of a metal-oxide composite material that contains at least 10 wt% of Ir, which contains one or more of Rh, Mo, Nb and Pt in a total amount ranging from 0.5 to 89.9 wt% and which also contains a rare earth oxide in an amount ranging from 0.1 to 15 wt%.