: Semibatch emulsion polymerisation is widely used for the production of a wide variety of polymer latices such as paints, adhesives, etc. Styrene-acrylic latices are made of styrene and acrylate monomers, which has many advantages. For example, it has wide source of raw materials, high function/price ratio, simple synthetic process and the latex has out-standing water resistance, alkali resistance, scrub resistance and also the paint film has good outdoor durable, adhesive attraction. So the styrene-acrylic latex has been widely used in building coating, metal surface coating and so on.The aim of this work is to synthesis water based ( Buthyl acrylate / Methyl methacrylate / Styrene ) terpolymer emulsions and ( Buthyl acrylate / Methyl methacrylate / Styrene / Clay ) nanocomposites for using in paint industry. So, viscosity, rate of drying, adhesion, flexibility and pencil hardness of latices were investigated. First series of experiments was carried out to reach a polymerization with high conversion (? 98%) by using a base formulation. In these experiments, feeding rate, temperature, initiator and emulsifiers concentration were variable parameters which were found 68gr/h, 85°C, 1wt% and 0.01545mole, respectively. In these series of experiments, Buthyl acrylate / Methyl methacrylate / Styrene monomers had weight ratio of 60/20/20 and the ratio of anionic to nonionic emulsifiers was also 50/50. At the second series of experiments, ratio of ionic emulsifier (sodium lauryl sulfate) to nonionic emulsifier (nonyl phenol polyoxyethylene glycol) at total concentration of 0.01545mole was changed and the properties of the prepared latices were investigated. The results indicated that the latex sample prepared by weight ratio of 30 to 70 of nonionic to ionic emulsifiers showed : 5 B adhesion, 1H pencil hardness, 2 mm flexibility and 7min drying time. These were acceptable properties compared with the other latex samples properties. Thus the effect of Cloisite-15A at various concentrations(1% , 2% , 3% , 4% , 5%) on this latex sample preparation and properties was studied. Mechanical properties of latex films were improved by in situ emulsion polymerization of ( Buthyl acrylate / Methyl methacrylate / Styrene / Clay ) and presence of nano particles on emulsion polymerization increased emulsion viscosity and time of film surface drying because of barrier properties of clay laminates. The highest conversion (? 97%) was obtained using 3wt% of Cloisite-15A. Then, by using a paint formulation made by REEF Company in Isfahan ( Known as Acrylic-367 ), paint samples were prepared. The properties of the nanocomposite paint films were measured. The results showed 5B adhesion, 4H pencil hardness, 2 mm flexibility and 9 min time for drying for paint made by nanocomposite contained 3 wt% Cloisite -15A was known as the best sample for paint application. FTIR spectra of ( Buthyl acrylate / Methyl methacrylate / Styrene / 3 wt% - Cloisite-15A ) nanocomposites showed shift of carbonyl peak from 1732 cm -1 to 1728 cm -1 and Al-O peak from 466 cm -1 to 461 cm -1 compared with the pure latex sample and clay indicating a good interaction between the nanoparticles and polymer segments. DSC results Also showed an increase in glass transition temperature of nanocomposite with 3wt% Cloisite-15A from -7?C to 19.5?C. Key words:Acrylic-Styrene emulsion, Emulsion polymerization, Nanocomposite, Water-based paint.