Abstract: PP/ABS blends and their composites filled by active micro-sized calcium carbonate (CaCO3) were prepared by a co-rotating twin-screw extruder using EVA (ethylene-vinyl acetate copolymer), SBS (styrene-butadiene-styrene) and PP-g-MAH (maleic anhydride grafted polypropylene) as compatibilizers. The effect of kinds and contents of compatibilizers on mechanical properties and processing fluidity were measured by melt flow rate instrument, electron universal testing machine and impact testing machine. The results showed that PP-g-MAH exhibited the best compatibilization on the PP/ABS blends. At the content of PP-g-MAH of 30 phr, the tensile and flexural strength of PP/ABS/CaCO3 composites increased by 42% and 37.5%, respectively. As the PP-g-MAH was used as compatibilizers, 60 % CaCO3 filled PP/ABS(70/30) blend has good mechanical strength and processing fluidity.