A spark plug for an internal combustion engine is provided which includes a housing, a porcelain insulator, a center electrode, and an annular ground electrode. The housing has a small-diameter portion which has a smaller inner diameter and defines a front end thereof. The ground electrode is secured to a front end surface of the small-diameter portion and forms a spark gap between itself and an outer periphery of the center electrode. The ground electrode is smaller in outer diameter than the front end surface of the small-diameter portion. A annular weld which joints the ground electrode and the small-diameter portion is formed in an annular boundary through which the front end surface of the small-diameter portion and the base end surface of the ground electrode face each other. The annular weld continuously and fully extends in a circumferential direction of the ground electrode.