The stabilization products often used to improve the support of granular layers in the construction of road surfaces may be expensive and difficult to get. Therefore, it is necessary to test different materials, which are cheap and easy to obtain, and which will enhance the physical and mechanical properties of pavement layers. This document evaluates the use of coal tar, as a stabilizer for granular subbase. Initially, with a description of tar properties, determining the optimal conditions for the granular subbase material compaction, by means of modified proctor tests and the calculation of the resistance of the unaltered material by using CBR lab tests (California Bearing Ratio). Afterwards, with the design and development of granular material mixes with different percentages of coal tar and determining its CBR as comparative parameter with that of the unaltered material. Finally, by calculating the optimal coal tar percentage in order to stabilize the subbase granular, the results showed an improvement in the resistance of the granular material and a decrease in its expansion due to the use of coal tar.