The protective effects of polymer additives, including a group of viscosity-enhancing polymer poly-gamma-glutamic acid (gamma PGA; 10, 50, and 500 kDa) and surface-active polymer Pluronic F68, on Chinese hamster ovary cells against damage due to shear stress were investigated in shake-flask cultures. The level of protection was dependent upon the molecular weight of gamma PGA and its concentration. When 0.05 or 0.075 % of 500 kDa gamma PGA was added, the cell growth and viability were almost equal to those of Pluronic F68 supplementation and were much higher than those of the control without additives. For the first time, we show that gamma PGA is another environmentally-friendly medium additive that can be used in place of Pluronic F68.