Abstract: Except for oil itself, the additives of lubricating oil are the major factors in producing foam. The foaming property was examined for every additive at different temperatures and concentrations in various base oils with different viscosities.To explain the foaming behavior with surface chemistry concept, the surface properties of the system in question were measured.It is assumed that the highly surface-active antifoaming agents adhere to the surface of the film to reduce its molulus of viscoelasticity and change the rhcological properties so as to defoam readily.