This paper presents the results of laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil under various types of loading. The soil samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14 %, 22 % and 29 %. A wetting-process tests were conducted in a modified triaxial cell on these soil. This procedure likes when a structure has been constructed and the degree of saturation of a foundation soil is increased (decreasing in matric suction). Four matric suctions were adopted; 100, 60, 30 and zero percentages of initial matric suction under two different mean net stresses; 100 kPa and 200 kPa. The changes in the degree of saturation may be due to rainfall, water table rising and/or leaking of sewage and water pipes. The results from this path revealed that the volumetric strains are increased with decreasing of the matric suction and increasing of the gypsum content

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