In this study, the effects of a road subgrade stabilized using black carbon on the rigid road pavement thickness and cost were investigated. For this purpose, pure soil was subjected to sieve analysis, hydrometer, consistency limits and pycnometer tests to determine its engineering properties. Afterwards, stabilized mixture samples were prepared by adding black carbon in five different ratios (2.5, 5, 10, 15 and 20%) to the soil. Pure and stabilized samples were subjected to the standard proctor test, maximum dry unit weights and optimum water contents were determined. Mixture samples prepared were subjected to unconfined compression and CBR tests after 28 days of curing period. Rigid road pavement thickness and cost were analyzed according to the AASHTO method using the data obtained. According to the test results, it was observed that the highest compressive strength was obtained from the mixture with 10% black carbon and the CBR value of the mixture at this ratio increased by 2.87 times compared to the pure soil. As a result, thanks to the soil stabilization using 10% black carbon, it was determined that the pavement thickness reduced by 3 cm and the rigid pavement cost by 9.68%.