A product formation model including growth associated and maintenance terms is developed for the growth of mammalian cells under Perfusion Chemostat(PC) cultivation. Two parameters in this model, growth asso-ciated term, α, and maintenance factor, β, are estimated for the production of tPA, EPO and pro-UK, and fitting these data with correlation factors of 0.90 to 0.93 for each case. It turned out that essential factors for cell growth, such as shear stress and dissolved oxygen tension play important role with respect to productivity, showing optimal values of 30-40% of dissolved oxygen tension and 20-50rpm of agitation speed for the production of EPO from recombinat CHO cells.