To provide a synthetic-resin sliding bearing that can reliably prevent dust or the like from entering a sliding surface, inhibits a reduction in a sliding characteristic caused by the entrance of dust or the like, in which hours of assembly work can be reduced, and that inhibits falling off easily due to vibration or the like.

The sliding bearing 1 includes: a synthetic-resin upper case 2 secured on a vehicle body side via an attachment member; a synthetic-resin lower case 3 overlapping with the upper case 2, and formed thereon a spring receiving seat surface for a suspension coil spring; a synthetic-resin sliding bearing piece 5 disposed in an annular space 4 between the upper case 2 and the lower case 3; and a synthetic-resin annular inside-seal member 8 and outside-seal member 9 for sealing both an annular gap 6 on an inner circumferential side in the radial direction X and an annular gap 7 on an outer circumferential side in the radial direction X between the upper case 2 and the lower case 3, both annular gaps connecting the annular space 4 with the outside.