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The condition of road access as a means of transportation needs to be considered because it affect the smoothness of vehicles passing over it. Road construction is not always on a good subgrade, there is possibility of being built on subgrade which has a low soil bearing capacity. If subgrade soil had low bearing capacity, the pavement will suffer damage such as holes and bumps. One of the parameters to find out the soil bearing capacity (soil strength)for subgrade is by Californian Bearing Ratio testing. Soil stabilization is one of some treatments to improve bearing capacity of soil through adding one or more material admixtures to the soil. This study aims to determine the effect of steel slag and fly ash admixture to the soil bearing capacity parameters such CBR value and its effect on soil physical properties. Soil samples are taken from location of Kadusentar Village Road Medong Village Mekarjaya Subdistrict Pandeglang District. The classification of soil using Unified Soil Classification System (USCS). The methode of stabilization of soil using variation of prosentase admixture 20% of fly ash and mixed with steel slag 0%, 10%, 20% and 30% from total weight of soil. Those samples are preservated for 0 day, 3 days, and 7 days then tested using CBR laboratory test apparatus. Based on the USCS, the classification of original soil sample in the area of study can be included as MH group, a non-organic clay soil with high plasticiy where its plasticity index value were 24,59%. The CBR laboratory test result showed that for variation of 20% fly ash and 20% steel slag with 7 days preservated give the optimum value of CBR increases from 3,524% to 26.14%. the highest CBR value of this mixture can be categorized as good classification. Plasticity index value decreased became 4.57 % which it can be categorized as low plasticity. Based on those results above it can be concluded that the addition of admixture combination of fly ash and steel slag can increase the CBR value and decrease the plasticity index value which is good for soil stabilization.