A spark plug for use in an internal combustion engine comprises a central electrode made of a base metal and an earth electrode. A tip portion is provided on the central electrode. The tip portion includes a noble metal tip layer for defining a spark discharge gap between the noble metal tip layer and the earth electrode, and an alloy layer provided between the noble metal tip layer and the central electrode. The tip portion is provided with grooves to be divided into a plurality of sections. The tip portion has an outer peripheral wall flared towards the earth electrode, and a width of the grooves gradually increases from a bottom thereof to a surface of the noble metal tip layer for defining the spark discharge gap.