An experimental study was undertaken to investigate the effect of plastic and granite waste powder on the geotechnical performance of expansive soil, using different mix ratios. The soil studied is Hachem, in the northwest of Algeria. In this context, reinforce the plastic powder with granite powder, then add the mixture to the expansive soil. The percentage of plastic powder is (0%, 1%, 2%, 3%, 4%) and reinforced at 2%, 4%, 6% and 8% with granite powder. The experimental results showed a gradual decrease in liquid limits, swell potentials, and swelling pressure as plastic and granite powder proportions increased. In terms of the results obtained by reducing swelling and swelling pressure values and increasing unconfined compressive strength (UCS) tests and ductility values, this mixture of waste plastics and granite can be of great importance in improving the mechanical properties of samples.