In this study, the tensile strength and M-Rockwell hardness of polycarbonate (PC)nanoalumina composites are investigated under various processing parameters. For this purpose, PC using a twin-screw extruder is melt compounded with nanoparticle of Al 2 O 3 in the presence of styrene-co-maleic anhydride (SMA) as the compatibilizer. Influences of weight percentage of nanoalumina and injection processing parameters including injection pressure and holding pressure (all in four levels) are investigated on tensile and hardness properties of nanocomposite samples using Taguchi's L 16 orthogonal array. The scanning electron microscopy (SEM) resultsreveal that an appropriate distribution of nanoparticles in polymeric matrix is achieved. According to the results, nanoalumina content is the most effective parameter on tensile strength and hardness with about 51% and 85% contribution, respectively. Results indicate that by addition 1.5 wt% of nanoalumina, the tensile strength and hardness of samples increase as much as 4.5% and 11%, respectively. Also, the results reveal that injection pressure and holding pressure are also effective parameters to change hardness and tensile strength. K E Y W O R D Smechanical properties, nanocomposite, polycarbonates, strength, styrene maleic anhydride