Polystyrene (PS) is a general-purpose glassy polymer with low cost and good processability, which is used extensively in polymeric products. The drawback of this polymer is its brittleness, which in turn limits its applications. In this research, Thermoplastic Elastomers of Polyurethane (TPU) was used to improve the mechanical properties of PS. Blends with different compositions were prepared using a twin-screw extruder and internal mixer. Test specimens for impact and tensile characterizations were obtained with an injection-molding machine and compression molding respectively. The results showed that increasing the amount of TPU leads to higher impact strengths and elongations at break of the blends. It was found that extruded and injected samples with TPU amounts bellow 20 wt. % leads to a rather smooth increase in the mentioned properties whereas in higher TPU contents (30-50 wt. %), the mechanical properties increase dramatically. On the other hand, tensile curves showed that adding only 10 wt. % of TPU changes the behavior of PS from brittle to ductile and therefore yielding occurred in all blends. Furthermore samples prepared by one-step and two-step method via internal mixer showed different trend of changing of mechanical behavior. In two step method,samples had better mechanical properties rather than extruded ones specially in samples with amount 10-30 % of TPU because different morphology. Scanning Electron Microscopy (SEM) showed a homogeneous dispersion of TPU particles in the PS matrix in all samples and the size of TPU domains increased by its higher amounts.Also samples prepared by two-step method showed sub-inculsion morphology which causes better impact strength.