A spark plug has a center electrode and an earth electrode. The center electrode is faced to the earth electrode so that a spark discharging gap is formed between the center electrode and the earth electrode. An electrode chip is formed on at least one of the center electrode and the earth electrode. The electrode chip has a composition containing 40 to 60 mol % of aluminum and iridium as a remainder thereof. In the composition of the electrode chip, it is possible to replace part of the iridium with 1 to 20 mol % of at least one metal selected from nickel, iron, cobalt, platinum and rhodium.