The mechanism of the flocculation of polyvinyl acetate suspensions by polycations was studied. The adsorption and neutralization data showed that almost all the surface charges were drawn, moved, and neutralized stoichiometrically by quaternary-poly-4-vinylpyridine(Q 3PVP). The possibility of bridging was nearly zero. The optimum flocculation occurred when almost all the surface charges were neutralized. The results from conductometric titration showed that the possibility of mosaic neutralization was also nearly zero. The optimum dosages increased with increasing added salts. The redispersion hardly occurred by Q 3PVP but occurred by polyethyleneimine(PEI) in high polymer concentration. A weak polycation such as PEI had smaller flocculating ability than a strong polycation such as Q 3PVP. From the results, it was concluded that charge neutralization was the predominant factor in the system.