The construction of engineering structures on weak soils may involve lots of risks due to differential settlement, shear failures and other instabilities. One of the main methods for stabilizing such soils is reinforcing them with tensile elements. Nowadays, regarding the production of massive amount of waste from industrial factories, their disposal is a challenging issue in environmental engineering. Thus many attempts have been made to use these materials for soil improvement purposes. Polypropylene fibers (PP fibers) are waste materials which attracted increasing attention in soil reinforcement applications. Nevertheless the combined effects of PP fibers and polymers on soil properties have not been inclusively discussed till now. The main aim of this research study was to investigate the effect of PP fibers and polymer admixture on the strength parameters of clayey soils both individually and in combined percentages using unconfined compression, direct shear and triaxial compression tests. In this context, PP fibers with 12 mm length mixed with the soil samples in contents of 0.3, 0.5, 0.75 and 1 percent by weight of dry soil. The PP fibers were white discrete short fibers. The polymer was an amino based powder called FTR-88 and added and mixed with soil in weight percentages of 5% and 8% to prepare samples for conducting different strength tests. Unconfined compression tests on the soil samples reinforced with PP fibers showed a significant increase in both unconfined compressive strength as well as failure strain while the soil stiffness decreased. Also, adding the FTR polymer in different percentages with three different curing times (6 hr, 1 day and 3 days) showed that unconfined compressive strength and stiffness of samples increased significantly. As the gel time of FTR polymer in water presence was only a few hours so the differences in strengths of samples with curing times of 1 and 3 days were negligible. It was also found that the samples with different percentages of PP fibers and polymer in various curing times gained more than 95% of their final strength only after 1 day. Moreover, the difference between final strength of samples with 5% and 8% polymer was less than 10%, so the 5% FTR polymer was suggested as an optimum content. The optimum percentage of fibers for achieving maximum strength was also found at 0.3%. The test results indicated that the inclusion of fiber reinforcement within non stabilized and stabilized soil caused an increase in the unconfined compressive strength. It was found that fiber content, polymer content and curing time had significant influence on the engineering properties of the fiber-polymer treated samples. Direct shear tests on soil samples reinforced with PP fibers showed that the reinforcement didn’t make a great change in the shear strength relative to the soil samples. However, the amount of increase in the soil cohesion was more pronounced in comparison with that of the internal friction angle. Conducting consolidated-undrained triaxial compression tests (CU) on clay samples with optimum content of FTR polymer (5 percent) and various amounts of PP fibers, it was found that the PP fiber content of 0.3% had the most increasing effect on the strength of samples. In addition, using combined additives of PP fibers and polymer in the soil samples showed much better effects than using them individually. Keywords: Stabilized soil, polypropylene fiber (PP), polymer (FTR-88), unconfined compression, triaxial compression (CU), direct shear tests