The findings of laboratory tests on the impact of matric suction on the compressibility of unsaturated gypsum sand soil under various percentages of adding Cement Kiln Dust (CKD) (1%, 3%, and 5%) are presented in this research. The soil samples were taken from Al-Najaf City in Iraq and had a 5% gypsum percentage. The results of the conducted tests depend on the saturation-unsaturation Oedometer device. In this paper, seven tests were performed. The first one was in saturated conditions and the second one was the Soil-Water Characteristic Curve (SWCC) to show the behavior of the wetting and drying paths. Then, depending on the initial matric suction that was calculated according to the field moisture content and the SWCC-wetting path, five unsaturated tests were done. The findings of these results are by increasing the matric suction, the volumetric strains are decreased, and the optimum percent of CKD material was 1%. This work could be used when dealing with such soil by using CKD materials as a west material.