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Swelling behavior of some soils, especially soils with high clay content, has a great impact on forest roads. Moisture variation in expansive soils results in their volume change. If the soil can not swell freely, it will apply pressure to surrounding structures which may eventually cause some damage or complete destruction. Therefore, it is essential to assess the swelling potential of the foundation soils and take appropriate measures to overcome such problem. In the present study, the effects of RPP as a polymer stabilizer to control swelling of expansive soils were investigated. For this purpose, different tests including Atterberg Limits, standard compaction, swelling potential, and swelling pressure, were conducted on control and treated soil samples using different Percentage of Polymer (RPP) (0.019, 0.04 and 0.06%). Also California Bearing Ratio (CBR) tests were conducted on control and treated samples based on manufacturer recommendation. To assess the effect of time on performance of polymer treated soil, samples with 0.019% RPP content were prepared and kept in sealed plastic bags for 7 and 14 days periods and then tested for Atterberg Limits, swelling potential and swelling pressure. The results showed that soil treatment with RPP, resulted in improvement of CBR and maximum dry density and reduction in Atterberg Limits, swelling potential and swelling pressure. The results also indicated that the curing 7–14 days periods had no significant effect on plasticity and swelling properties of the treated samples.