A pneumatic tire comprising two circumferential main grooves (5, 6) within a tread ground-contact width (TWh), and a group of polygonal blocks (Gb) between the two circumferential main grooves (5, 6), in which the group of polygonal blocks (Gb) is comprised of a plurality of polygonal blocks arranged in at least two longitudinal rows in a tire circumferential direction and in a plurality of transverse rows in a tire width direction, the polygonal blocks each having not less than five sides and being defined by narrow grooves (3a, 3b), wherein: the polygonal blocks in the adjacent longitudinal rows are arranged so as to be staggered from each other in the tire circumferential direction; the group of polygonal blocks (Gb) has a widthwise center (GbC) that is positioned within a fifty-percent-wide region of the tread ground-contact width (TWh) across a tire equatorial plane, and the pneumatic tire including side block rows each comprised of a plurality of side blocks defined by the circumferential main grooves (5, 6), widthwise grooves (7, 8) and the narrow grooves (3a, 3b) and arranged in the tire circumferential direction, the side block rows being arranged on both sides in the tire width direction across the group of polygonal blocks (Gb) respectively, wherein: the side blocks are each formed so as to have a larger ground-contact area compared with the polygonal blocks; the ground-contact areas of the side blocks arranged on both sides of the group of polygonal blocks (Gb) have a different dimension respectively; and the side blocks arranged in the outer side in the tire width direction within the blocks on both sides across the group of polygonal blocks (Gb) each have a larger ground-contact area. the polygonal blocks in the adjacent longitudinal rows are arranged so as to be staggered from each other in the tire circumferential direction; the group of polygonal blocks (Gb) has a widthwise center (GbC) that is positioned within a fifty-percent-wide region of the tread ground-contact width (TWh) across a tire equatorial plane, and the pneumatic tire including side block rows each comprised of a plurality of side blocks defined by the circumferential main grooves (5, 6), widthwise grooves (7, 8) and the narrow grooves (3a, 3b) and arranged in the tire circumferential direction, the side block rows being arranged on both sides in the tire width direction across the group of polygonal blocks (Gb) respectively, wherein: the side blocks are each formed so as to have a larger ground-contact area compared with the polygonal blocks; the ground-contact areas of the side blocks arranged on both sides of the group of polygonal blocks (Gb) have a different dimension respectively; and the side blocks arranged in the outer side in the tire width direction within the blocks on both sides across the group of polygonal blocks (Gb) each have a larger ground-contact area. the side blocks are each formed so as to have a larger ground-contact area compared with the polygonal blocks; the ground-contact areas of the side blocks arranged on both sides of the group of polygonal blocks (Gb) have a different dimension respectively; and the side blocks arranged in the outer side in the tire width direction within the blocks on both sides across the group of polygonal blocks (Gb) each have a larger ground-contact area.