In this paper, PP/EPDM nanocomposites with 5 wt% nanoclay are fabricated by friction stir processing (FSP) and compared to the results obtained via a conventional twin screw extruder (TSE). Also, the effects of process parameters of these process on morphology and mechanical properties of this nanocomposites are investigated using Taguchi analysis. The prepared PP/EPDM/clay nanocomposites by two methods were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and mechanical property tests. Comparison of the results of these methods indicated that PP/EPDM/clay nanocomposite fabricated by FSP had a better dispersion of nanoclay and mechanical properties. The results show that by addition of 5 wt% nanoclay to the base material, the tensile strength and tensile modulus of FSP sample are 12% and 8% higher than the TSE sample. The TGA results shows that, the temperature at 50% weight loss for PP/EPDM blend is 382°C. While this temperature for TSE and FSP samples are 395°C and 406°C, respectively. Under optimal conditions of rotational speed of 1,200 rpm, traverse speed of 50 mm/min, shoulder temperature of 100°C and number passes of 3, simultaneous maximization of tensile strength (19.35 MPa), tensile modulus (643 MPa), impact strength (63 J/m) and elongation at break (101%) can be obtained. POLYM. COMPOS., 40:3306–3314, 2019. © 2018 Society of Plastics Engineers