A pneumatic tire includes a tread surface having a middle rib defined by a first circumferential groove and a second circumferential groove in its center region. Middle lateral grooves, that obliquely extend in the widthwise direction of the tire, are disposed at predetermined intervals in the tire circumferential direction in the middle rib; only one terminal end of each middle lateral groove communicates with one circumferential groove of the first and second circumferential grooves. An assistant groove is provided between each of adjacent middle lateral grooves; the assistant groove extends in such an inclined manner that the inclination direction thereof with respect to the tire circumferential direction is opposite to that of the middle lateral grooves; a block is defined by the assistant groove, middle lateral grooves and one circumferential groove. The middle lateral grooves each include a first inclined groove portion having an inclination angle a ranging from 35 degrees to 60 degrees and a second inclined groove portion having an inclination angle β ranging from 0 degree to 30 degrees.