A pneumatic tire comprises a tread portion provided between the tire equator and each tread edge with a continuous main circumferential groove and outer lateral grooves, the outer lateral grooves including alternately arranged wide lateral grooves and narrow lateral grooves each extending axially outwardly from the main circumferential groove, the axially inner groove-wall of the main circumferential groove extending substantially straight in the circumferential direction, the axially outer groove-wall of the main circumferential groove comprising circumferential portions and inclined portions, the circumferential portions extending substantially straight so that the width of the main circumferential groove is substantially constant, and the inclined portions inclined so that the width of the main circumferential groove increases from the narrow lateral grooves to the wide lateral grooves.