Abstract: Here the protective effect and mechanism of serum and Plurc ic F68 on hybridoma cells in suspended cultures were examined and analyzed by.a series of experimental and theoretical studies.It is,found that serum and Pluronic F68 do not Show and protection on cells when the Kolmogorov turbulent eddy sizes of the bulk liquid in bioreactors are similar to or smaller than the cell size. However,if the gas bubbles are the major source to result in cell damage,their potective effect is very significant.Particularly,Pluronic F68,at its concentration of lg/L provides full prevention to cells from damage by bubbles. The results of foam fractionation experiments,thermodynamic analysis and surface tensioin measurements demonstrate that the protective effect of serum and Pluronic F68 on cells is based on their surface activities,in which they eliminate cell damage by changing the interfacial properties of the system to prevent cell-bubble adhesion.