A series of particulate polymeric composites filled with precipitated calcium carbonate (PCC) were prepared via a twin screw mixer with different particle content. The effects of PCC of varying particle size (80 nm, 1.5 µm), content ( 0-30 wt%), type of surface modification (uncoated, stearic acid coated) and particle size distribution on the physical properties, mechanical behavior, processability and rheological response of composites were investigated. PCC particles are more widely used as functional filler in the polymer field and improve processing conditions as a rheology control agent. Crystallization studies indicate that fine PCC acts as a good nucleating agent for polymeric matrix with crystalline structures. Results of physical and mechanical investigations highlight the outstanding properties of fine PCC particles. The mechanical efficiency of PCC for polymeric composites were found to depend strongly on its purity, type of surface treatment and average particle size. Interestingly, using surface modified calcium carbonate in particulate polymeric composites not only have reduced the cost, but also have made a high improvement of both stiffness and toughness as well as dimensional stability. Notched Izod and falling weight impact data presented a significant increase of impact resistance of filled composites. By taking all variables into consideration one can, not only optimize a compound’s performance, but also lower its cost. Keywords: Particulate composite, precipitated calcium carbonate, compound, surface modification, functional filler, nucleating agent.