Large amout of liquid effluents are daily generate by dairy industries, the formation of a stable oi-in-water emulsion may occur, making difficult the oil separation. This project aimed to understand the action mechanism of chitosan with different molecular weights on the de-emulsification of oil in water emulsions for application on the treatment of wastewater from dairy products. Obtained results showed that de-emulsification using chitosan was not expressive for oil separation, however, induced whey protein separation from aqueous phase.