The stabilization of optimum pH for cells can cause a higher erythropoietin (EPO) production rate and a good growth rate with the prolonged culture span in recombinant Chinese hamster ovary (r-CHO) cells. Our strategy for stabilizing the optimum pH in this study is to reduce the lactate production by adding sodium lactate to a culture medium. When 40 mM sodium lactate was added, a specific growth rate was decreased by approximately 22% as compared with the control culture. However, the culture longevity was extended to 187 h, and more than a 2.7-fold increase in a final accumulated EPO concentration was obtained at 40 mM of sodium lactate. On the condition that caused the high production of EPO, a specific glucose consumption rate and lactate production rate decreased by 23.3 and 52%, respectively. Activity of lactate dehydrogenase (LDH) in r-CHO cells increased and catalyzed the oxidation of lactate to pyruvate, together with the reverse reaction, at the addition of 40 mM sodium lactate. The addition of 40 mM sodium lactate caused the positive effects on a cell growth and an EPO production in the absence of carbon dioxide gas as well as in the presence of carbon dioxide gas by reducing the accumulation of lactate.