Effects of calcium carbonate (CaCO3) and compounding sequence on the phase morphology of maleic anhydride-grafted polypropylene (MAPP) compatibilized polyamide 6 (PA6)/polypropylene (PP) blend were investigated. The morphology in the subskin and core regions of injection molded specimen was observed using scanning electron microscopy, which shows great changes due to the incorporation of CaCO3. With the addition of CaCO3 (25 phr), oriented ginger-like network (directly mixing) or loose elongated network (mixing PA6, PP, and MAPP with premixed PA6/CaCO3 masterbatch) of PP phase is formed in the core region, instead of spherical dispersed PP domains for unfilled blend. The distribution of CaCO3 in PA6 and PP phases was determined by selectively dissolving PA6 phase and thermogravimetric analysis of PP phase. A possible mechanism is proposed based on the morphology evolution process to interpret the morphological differences. The mechanical properties and heat distortion temperature of the materials were tested and correlated with the morphology formed. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013