An objective is to provide a spark plug in which a ground electrode has a protrusion formed from the same material as that used to form the ground electrode and the heat transfer performance of the protrusion is improved to thereby improve erosion resistance. A spark plug 1 includes a rodlike center electrode 5 extending in the direction of an axis CL1; a substantially cylindrical insulator 2 provided externally of the outer circumference of the center electrode 5; a substantially cylindrical metallic shell 3 provided externally of the outer circumference of the insulator 2; and a ground electrode 27 extending from a front end portion 26 of the metallic shell 3 and forming a spark discharge gap 35 between a distal end portion thereof and a front end portion of the center electrode 5. A protrusion 28 projecting toward the center electrode 5 and forming the spark discharge gap 35 in cooperation with the front end portion of the center electrode 5 is formed at the distal end portion of the ground electrode 27 from the same material as that used to form the ground electrode 27. At least the protrusion 28 has an average crystal grain size of 20 μm to 200 μm inclusive.