A thrust bearing for receiving an axial force of a crankshaft of an internal combustion engine. The thrust bearing includes a pair of half thrust bearings having a semi-annular shape that form an annular shape by abutting their circumferential end surfaces. Each half thrust bearing include thrust reliefs formed adjacent to both circumferential end portions of a sliding surface receiving the axial force so that a wall thickness is thinner toward the circumferential end surface. A thrust relief length L2 at an inner end portion of the thrust relief positioned on a rear side of one of the half thrust beings in a rotational direction is larger than a thrust relief length L1 at an inner end portion of the thrust relief positioned on a front side of the other of the half thrust bearing in the rotational direction.