The study aims to determine the bearing capacity of the soil stabilized with Portland cement and fly ash as well as obtaining the mixing percentage of stabilizing agent to increase the bearing capacity of the soil. Soil testing sediment of dredging at Bili-Bili DAM is conducted with several characteristics properties, they are: testing the water content, bulk density, density, limits of Atterberg, sieving and testing of minerals and chemicals, while density testing is used for fly ash and Portland cement, then the process of stabilization or mixing. The variations of the mix: Soil sediments, cement (5%, 10%, 20%), fly ash (2.5%, 5%, 10%), then mechanical testing which consists of compaction, CBR, and unconfined compressive strength. The results of properties testing of water content, bulk density, specific gravity, are 97.13%, 1.61 g / cm3, and 2,51gr / cm3. In addition to the mineral and chemical content testing is to determine the content of the soil sediment, fly ash, and the mix between them. The test results of CBR and Unconfined Compressive Strength show that the variations in soil sediments (native) compared with the variation of mixture with the addition of Portland cement and fly ash have higher value than the soil sediment (original) and keep increasing up to a variation of a mixture of 20% Portland Cement + 10% fly ash. From these results, it can be concluded that the value of the soil bearing capacity of sediment dredged at DAM Bili-bili without stabilization Portland Cement and Fly Ash obtained CBR value and Unconfined compressive strength (UCS) are quite low, but with the stabilization of Portland cement and fly ash CBR value and Free Compressive Strength (UCS) have increased continuously with the addition of the composition of the Portland cement and fly ash. Where the greatest value of CBR and Unconfined Compressive Strength Portland Cement stabilization are at 20% and 10% fly ash.