Provided is a pneumatic tire that can provide high-speed durability, high-speed steering stability, and shock burst resistance in a highly compatible manner while reducing the number of carcass layers to reduce a tire weight. In the pneumatic tire including one carcass layer (4) and a tread portion (1) made up of a cap tread layer (11) and an under tread layer (12), an under tread layer (11) is made up of a rubber composition having hardness at 20°C ranging from 60 to 65, tensile stress at 100% elongation at 100°C ranging from 2.0 MPa to 4.0 MPa, and a product of tensile strength at 100°C and an elongation at break at 100°C of 2000 or more, the carcass layer (4) is made of an organic fiber cord having an elongation ratio under a load of 1.5 cN/dtex on an inner circumferential side of a belt layer ranging from 5.5% to 8.5% and an elongation at break ranging from 20% to 30%, and a product A = D × Ec of a fineness based on corrected mass D per carcass cord and an insertion count Ec is set to from 1.8 × 10 5 dtex/50 mm to 3.0 × 10 5 dtex/50 mm.