Expansive soils have the inherent property of swelling when they have adsorbed water and shrinking when they are dried. This property of expansive soil causes to damage structures constructed on it. To minimize the impact of the expansive soil, it is necessary to improve existing soil before commencing infrastructural construction activity. This study aims to make metakaolin as a partial replacement of cement for the improvement effect of expansive soil on the soil water characteristics curve. From three test pits, samples were collected from Debre Tabor City and tested for identification and characterization. The soil was improved with cement content of 3%, 5%, 8%, and 10% by the dry weight of the soil. The results show that the optimum cement content was obtained 10% and replace half of the optimum cement content was by metakaolin with the amount of 5%,8%,11%,14%.,7%,20%,23% 26% and 29%. The optimum combined additive decreases the plasticity index from 64.76% to 27.5%, free swell index from 134% to 45%, maximum dry density from 1.33 g/cm3 to 1.36 g/cm3, California bearing ratio value from 1.28% to 5.15% at 5% cement and 17% metakaolin. The addition of metakaolin, cement and metakaolin-cement with the various ratio on the high plastic expansive soils was resulted to a significance effect on the SWCC of the metakaolin-treated, cement-treated and metakaolin-cement-treated expansive soil. The result showed that SWCC can be used for the evaluation of treatment method. The soil stabilization by using metakaolin, cement, metakaolin-cement decrease the value of fitting parameter “a” which can show the inflation point. This is due to the formation of aggregates and increase pore size in the soil structure. The AEV of the treated soil decrease with the percentage of stabilizers increase. And the SWCC shifts to the left or low suction value. The fitting parameter “n” is an indicator of the soil’s desaturation capacity and the increment or decrement of soil pore size distribution. From the result of the study the “n” value was increase as the percentage of the stabilizers increase and the soils desaturation increase as the same fashion with “n”. Keywords- Soil Suction, Unsaturated Soil, Soil Water Characteristic Curve (SWCC)