A thrust sliding bearing 1 includes: a synthetic resin-made upper casing 3 which has a vehicle body-side seat surface 10 for a mounting member 8 on a vehicle body side and an annular lower surface 2; a synthetic resin-made lower casing 5 on which an annular upper surface 4 opposed to the annular lower surface 2 and a spring seat surface 25 for a suspension coil spring 7 are integrally formed, and which is superposed on the upper casing 3 so as to be rotatable about an axis O of the upper casing 3 in an R direction; and a synthetic resin-made thrust sliding bearing piece 6 which is disposed in an annular gap 9 between the annular lower surface 2 and the annular upper surface 4, and has an annular thrust sliding bearing surface 51 which slidably abuts against at least one of the annular lower surface 2 and the annular upper surface 4.