To provide a cast iron composition for an automobile engine exhaust system which can increase high temperature oxidation resistance and high temperature strength, further can improve durability and reliability, and can minimize the damage to a catalyst caused by oxidized scale.

The cast iron composition for an automobile engine exhaust system is obtained by using iron as the main material, and incorporating, by weight, 2.9 to 3.8% carbon (C), 4.0 to 4.5% silicon (Si), ≤0.3% manganese (Mn), ≤0.05% phosphorus (P), ≤0.1% sulfur (S), 0.8 to 1.2% molybdenum (Mo) and ≤0.025% magnesium (Mg) therein.