In the construction site, an improved ground may be exposed to wetting and drying repetitions with rainwater even if we assume it is under air-dried condition. This paper describes the effect of wetting and drying repetitions on unconfined compressive characteristics of cement-stabilized soils mixed with bassanite produced from waste plasterboard. As a result, the unconfined compressive strength of cement-stabilized soils mixed with bassanite with wetting and drying repetitions is about 90% of those under air-dried condition although the unconfined compressive strength of cement-stabilized soil with wetting and drying repetitions decreases to about 70-80% of those under air-dried condition. Bassanite produced from waste plasterboard is effective as improver for soils even if improved soils are exposed to wetting and drying repetitions.