In this study in order to the synthesis of poly (methyl methacrylate-co-butyl acrylate-co-acrylic acid) / Nano silica Nanocomposite at first, some samples of poly (methyl methacrylate-co-butyl acrylate-co-acrylic acid) were prepared by Seeded Semi-batch in-situ Emulsion Polymerization technique with mixed nonionic(NP20)/ anionic(SDS) emulsifier system in several ratios. The weight ratio composition of monomers [MMA: BA: AA] in initial charge (which makes latex primary particle) and pre-emulsion respectively adjusted at [1: 0.96: 0] and [1: 0.95: 0.03] for all samples. The overall monomer conversion (reaction efficiency) and coagulum percentage was measured for all samples and the most Desirable formulation due to the overall conversion (97% ) and the coagulum (0.04%) was chosen for the synthesis of poly (methyl methacrylate-co-butyl acrylate-co-acrylic acid) / Nano silica so that have Suitable mechanical physical properties for use as a water-based acrylic binder. In the following section of this research, Seeded Semi-batch in-situ Emulsion Polymerization of methyl methacrylate, butyl acrylate and acrylic acid Accomplished in the presence of 1, 2 and 3% by weight (relative to the total weight of monomers) silica nanoparticles and Eventually Nano composite Latexes were obtained with high final conversion (95% ), low coagulum ( 0.09%), short drying time and stable for more than 6 months. Characterization of synthesized Nano composite acrylic terpolymers performed by Fourier transform infrared spectroscopy (FTIR). The size and distribution of Nano composite latex particles measured by dynamic light scattering (DLS) Because of its importance effect in ultimate properties of its film. Also the Z-average (hydrodynamic diameter) of latex particles was obtained, and showed that increasing in Nano silica concentration causes decreasing of z-average from 240 nm to 154 nm respectively for silica-free sample and the sample containing 3% silica. While the particle size distribution index (PDI) increased. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) elemental map of Si, O, C and DLS results proved that the distribution of Nano silica particles is appropriate in the matrix. The roughness of fracture surface of Nano composite sample containing 2 wt. % silica nanoparticles was dramatically more than the free-silica sample. Contact angle test used for assessing changes in the hydrophilic/hydrophobic property of Nano composite samples surface, the results showed a direct relationship between the percentage of silica and the contact angle. The results of measuring the drying time Revealed that increasing concentrations of each reaction (typically this study) variables such as anionic/nonionic emulsifiers and Nano silica will prolong the process of drying latex film formation. The dynamical-mechanical behavior of poly (methyl methacrylate-butyl acrylate-acrylic acid) / silica was evaluated using DMTA then obtained E', E "and tan ? curves interpreted for molecular dynamics behavior study through the effect of Nano silica particles.