Side-reinforcing rubber composition and run flat tire using the same

The present invention provides a side-reinforcing rubber composition for a run flat tire, which achieves both low heat generating properties and high strength and improves run flat durability, and a run flat tire using the rubber composition. Specifically, the present invention provides to a side-reinforcing rubber composition for a run flat tire comprising 10 to 100 parts by weight of carbon black having nitrogen-adsorbing specific surface area of 30 to 100 m/g and dibutyl phthalate oil absorption of at least 50 ml/ 100g, 5 to 120 parts by weight of a laminated natural mineral having aspect ratio of 3 to 30 and average particle size of 2 to 30 mu m, and at least 2 parts by weight of sulfur or a sulfur compound, based on 100 parts by weight of a diene rubber component, and a run flat tire using the composition as a side-reinforcing rubber.