The present invention aims to provide a honeycomb structural body which is high in mechanical strength, has no cracks even when a thermal stress is generated, is less susceptible to generation of cracks or damage and is excellent in durability even in the case where a high pressure is applied from an outer peripheral face thereof, and is excellent in push-out strength. The honeycomb structural body of the present invention is a honeycomb structural body which has irregularities formed on an outer peripheral face thereof and that of a ceramic block, wherein when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of the honeycomb structural body, a center-of-gravity thereof is defined as c1, a distance between a minimum concentric circumscribed curve, having c1 as the center-of-gravity, of the least square curve and the center-of-gravity c1 is defined as D1, a distance between a maximum concentric inscribed curve, having c1 as the center-of-gravity, of the least square curve and the center-of-gravity c1 is defined as D2, and (D1 - D2) is defined as M1, the following inequality is satisfied: 0.3 mm ‰¤ M1, and when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of the ceramic block, a center-of-gravity thereof is defined as c2, a distance between a minimum concentric circumscribed curve, having c2 as the center-of-gravity, of the least square curve and the center-of-gravity c2 is defined as D3, a distance between a maximum concentric inscribed curve, having c2 as the center-of-gravity, of the least square curve and the center-of-gravity c2 is defined as D4, and (D3 - D4) is defined as M2, the following inequality is satisfied: 0.5 mm ‰¤ M2 ‰¤ 7.0 mm.