A pneumatic tire is provided which includes a carcass extending between bead portions, and a belt disposed radially outside the carcass in the tread portion. At least one of the carcass and belt includes a cord ply of a polyethylene-2,6-naphthalate fiber cord. The polyethylene-2,6-naphthalate fiber cord has a total denier number of from 2500 to 3600, a twist number of from 30 to 40 turns/10 cm, an initial stage modulus at 25 deg. C. in a range of from 50 to 65 gf/d, and a variation of the initial stage modulus at between 25 to 70 deg. C. which is not more than 20% in absolute value.