In this study, the mechanical properties of composites of poly (vinyl chloride) (PVC), as one of the most important thermoplastic, ??are investigated. PVC has high mechanical strength, high corrosion and chemical resistance and relatively low cost. But it has weak impact resistance which limits its application in some areas. The main object of this research is to improve interfacial interaction between the CaCO 3 particles and the matrix for promotion of impact strength of the polymer. At the start of this study a direct dry mixing of PVC and nano CaCO 3 particles was found to be efficient using XRD and SEM. In the next step the effect of surface treatment (by MPTS and PMHS) of CaCO 3 on mechanical properties (impact strength, tensile strength, elongation at break and Young modulus) of PVC composite samples, using various mass ratios of treated micro and nano-CaCO 3 particles, was studied. The appearance of the bands at 1041.5 and 1126.3 cm -1 was indicative of the formation of Si-O-CaCO 3 bond on CaCO 3 particles. The maximum impact strength, elongation at break, tensile strength and Young’s modulus were obtained at 9/6 mass ratio of (micro/nano)-CaCO 3 in the PVC matrix. SEM images of fractured surfaces of tensile test revealed fibrils. Agglomeration of particles was observed with increase in content of micro CaCO 3 particles resulting in lower mechanical properties. In the continuation of this study, The treated particles of CaCO 3 were encapsulated by poly(butyl acrylate-co-methyl methacrylate) through in situ emulsion copolymerization using different mole ratios of butylacrylate (BA)/merthyl methacrylate (MMA). FTIR spectra of the extracted synthesised samples showed chemical grafting between the treated particles and the polymer through C-S bonding at wavenumber 754.1 cm -1 . Polymerization conversion and binding efficiency of core-shell particles were over 92% and 94%, respectively. TEM revealed that in the core-shell structure, the particle size for nano and micro was 72-87 and 175-192 nm, respectively. The synthesized core-shell particles were melt blended with PVC using a constant content of micro and nano core-shell particles (15 phr). The mechanical properties showed that impact strengths of PVC with micro and nano core-shell particles were 3.3 and 18 times more than pure PVC, respectively. Tensile strength and elongation at break showed a very slightly decrease and significantly increase, respectively. SEM of fractured surfaces of impact test showed a relatively smooth and featureless surface for low mole ration of BA/MMA and for the high mole ratio of BA/MMA monomers, the morphology of PVC core-shell composites looked like a “honeycomb” structure, and a large number of fibrils and voids were presented on the surface of impact test specimens. The fractured surfaces of tensile test revealed that the high mole ratio of BA/MMA monomers in core-shell particles induced shear bands and the low mole ratio of BA/MMA induced crazes in PVC/nano-CaCO 3 -poly(BA-co-MMA) composites. According to Molau test, interfacial interaction between PVC and core-shell particles was enhanced. FTIR spectra of pure PVC and PVC/nano-CaCO 3 -acrylic resin composites illustrated hydrogen bonding interaction between carbonyl groups (C=O) of the resin and hydrogen of CHCl groups of PVC chains. Keywords: PVC, Calcium Carbonate, Micro and Nano Particles, Core-Shell Particles, Mechanical Propertie