Simulation and optimal design of the reactor for the seeded continous emulsion polymerization process have been done in this work. An internal mixer (Toray Hi-Mixer) as seeder connected with a stirred tank is designed to correlate conversion, molecular weight, and MWD with the model simulation proposed. An optimal mean residence time of seeder \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _s)_c$\end{document} is found to lie between \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _1)$\end{document} and tin, where \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _1)_{{\rm opt}} = (3aS_0 /2r\eta N_a \alpha)^{3/5}$\end{document} and tin = 1.57(aS0/riηNA)3.5. The optimal design of the process is performed according to the above relations under several polymerization conditions. In general, the increase in number of stages inside the seeder can reduced the volume of CSTR for a required production. Molecular weight of products is increased by increasing the number of stages inside the seeder, by decrasing the concentration of the initiator, and by increasing the concentration of the emulsifier under the optimal conditons.