The effects of hydrophobic agents on aqueous foam stability were studied in the presence of an antifoamer, based on the destabilization mechanisms of aqueous foam. The stability of the foam film was dependent on both film rheology and structural modification by the hydrophobic agents, tertiary butyl phosphate (TBP) and lecithin. The hydrophobic agents reduced the elasticity of the foam film and the surface activity of the surfactant that stabilize the foam film. TBP effectively accelerated the film drainage and destabilization process of the foam film by depleting the surfactant. When the amount of TBP added is very high (above 500 ppm), the TBP generated colloidal hydrophobic drops inside the film phase. The TBP drops penetrated the film surface and spread on the surface during the film drainage. The TBP drops were accumulated and became larger in the Plateau border and effectively broke the foam. A new understanding of the TBP role on the antifoaming action is postulated.