Although a number of investigations have been devoted to the analysis of silica or carbon black filled elastomer networks, little work has been done on the reinforcement of CaCO3 filled elastomer network. In this work, the reinforcement of polydimethylsiloxane (PDMS) network by using CaCO3 nano-particles was investigated. We have found a simultaneous increase of tensile strength, modulus and elongation with the increase in nano-CaCO3 content, which suggests that nano-CaCO3 particles can indeed be used as a reinforcing agent, just like silica or carbon black. Interestingly, the tensile strength, modulus and elongation were seen to leave off for the first time when the content of nano-CaCO3 particles reaches to 80%. PDMS also showed an enhanced elastic modulus and storage modulus with the increase in nano-CaCO3 content, particularly for samples with high nano-CaCO3 content. SEM was used to investigate the dispersion of the filler in PDMS matrix. A better dispersion was found for samples with high nano-CaCO3 content. A great increase of viscosity was found for samples with higher filler content, which is considered to be the reason for the good dispersion thus the reinforcement, because high viscosity will be helpful for breaking the agglomerates of fillers into small size particles under effect of shear. Our work provides a new way for the reinforcement of elastomer by using an adequate amount of nano-CaCO3 particles instead of a small quantity of silica, which is not only economically cheap but also very effective.