An oil-impregnated sintered sliding bearing formed of a porous iron-based sintered alloy with quenched structure and receiving a high surface pressure capable of reducing the number of finishing steps by cutting and grinding and providing a bearing performance equivalent to or higher than that of conventional bearings, wherein a plurality of irregular lines having a height difference of 2 to 12.5 μm extending in circumferential direction are axially arranged parallel with each other by cutting the inner peripheral surface thereof to form a swelling surface in axial direction, and the portion thereof deeper 10 to 60μm than the front layer of the inner peripheral surface is formed dense to seal surface pores so as to reduce the pores opening to the front surface to 1 to 10 percent of area, whereby the bearing can be used at a surface pressure of 6 kgf/mm2 (58.8 MPa) or higher and a sliding speed of 2 to 5 cm/s.