Masterbatch dilution was utilized to prepare polystyrene/carbon nanotubes (PS/CNT) nanocomposites for microinjection molding (mu IM). The effect of processing parameters, such as injection velocity and melt temperature, on the microstructure and electrical conductivity of injection molded microparts was systematically investigated. The electrical conductivity of the microparts was measured in three perpendicular directions to determine anisotropy. Results showed that the measured conductivity is process-dependent and melt temperature is the main factor that affects the electrical conductivity of the resultant samples. Electrical conductivity increased with an incremental loading fraction of CNT, and the percolation threshold shifted to higher filler loading concentration which was ascribed to the very high shear rate in mu IM. In addition, Raman analysis, SEM observations, and simulation results indicated that CNT is preferentially oriented along the flow direction arising from the high shearing effect induced by mu IM. POLYM. ENG. SCI., 56:1182-1190, 2016. (c) 2016 Society of Plastics Engineers