This paper presents the effects of processing parameters and submicron core-shell rubber particle filler on the mechanical properties and cell morphology of microcellular injection molded polyamide-6 (PA-6) composites. Three types of materials are studied, namely, neat PA-6 resin, and 0.5 wt% and 3.1 wt% core-shell rubber polybutylacrylate-polymethylmethacrylate-filled PA-6 composites. This study shows that the addition of a small amount (0.5%) of coreshell rubber particles improved the ductility and impact strength of microcellular injection molded PA-6 samples. In comparison to the microcellular injection molded PA-6 polymer-clay nanocomposite, the samples with a small amount (0.5%) of core-shell rubber had much higher impact strength and ductility. The small addition of core-shell rubber also reduced cell size and increased cell density of the microcellular injection molded PA-6 parts, in comparison to their neat resin counterparts. On the other hand, at higher core-shell rubber loading, the cell size and density were found to be similar to that of the neat resin.