Ternary polymer blends of PP/PA6/PS were prepared by melt blending using a co-rotation twin-screw extruder with a screw diameter of 35 mm and L/D ratio of 48. The screw rate was set at 120 rpm. The barrel of the extruder has seven temperature-control zones and their temperatures were set at 190–200–210–220–230–230–220 °C (from hopper to die). Before blending, the compositions were dried in a vacuum oven at 80 °C for 10 h and used immediately. The weight ratio of (PP + compatibilizers)/PA/PS is fixed at 50/25/25. Based on formulation of the blends with PP-g-(MAH-co-St) as compatibilizer ((PP + compatibilizer)/PA/PS = (45 + 5)/25/25), each of blends has almost same functional group content in mole ratio. The palletized blends were dried and injection moulded into standard ASTM specimens using a ZT-630 injection moulding machine for mechanical tests.