Cement kiln dust (CKD) is a by-product of the cement factories that improves poor sub grade conditions with technical, economic and environmental benefits. There are about 20 cement plants in Ethiopia that can generate 15%-20% of CKD from the production of cement and clinker. Usually, cement, lime, bitumen, and blast furnace slag are universal stabilizers, which are used in the construction of roads. This study used unprocessed CKD by adding it to poor sub grade soil to examine how poor sub grade soil could be improved. Sampled CKD was obtained from inside and outside of the Dejen Cement Factory whereas the soil sample was taken from Chis-Abay, which is ERA's proposed asphalt highway project. For this study, the researcher adopted AASHTO T 193 designation. With this method, sampled soil, which comprises CBR value, OMC and MDD (with a different dry weight of CKD from 5% with a 5% interval up to 30% by soil weight) was employed. Through comparative evaluation, the result indicated that the dose of CKD from inside the factory at 20% within 7 curing days improved the CBR value from 1.1% to 54.33%. On the other hand, the 20% of CKD from outside the factory, achieved 29.27% of CBR value has shown a decrease in performance. When 15%-20% of CKD from inside the factory was used, the thickness of the road layer decreased by 400-600 mm. Thus, it saved a cost of 37.4-137.31 in Birr/m2. The higher cost reduction is for a rigid pavement design. Even, adding 15% of CKD to untreated weak soil on HMA flexible pavement could be enough to decrease the required thickness. For a soil with a swell of greater than 7.5%, could not achieve the specified swell need by using the CKD amount less than 25%; whereas, soil with a swell less than 7.5% can achieve the minimum swell requirement by using the CKD amount greater or equal to 15% with 14 days curing effect. The 14 days of curing effect is applied only for a swell on the mix, which has an amount of 15% CKD.