To provide an excellent oral drug delivery technique utilizing an oil particle-absorbing action in a constant animal digestive canal.

This method for administering the physiologically active substance is characterized by preparing an oil-in-water type emulsion whose oil drops are fine oil particles containing the physiologically active substance and having an average particle diameters targeted for an oil sphere-absorbing action in the digestive canals of animals, and then orally administering the emulsion to a non-human animal whose oil particle-absorbing action has been recognized. In the fine oil particles in the emulsion, the physiologically active substance is buried in the oil phase by the action of an oil-soluble emulsifier as such or while forming an extremely fine dispersion phase together with a small amount of water.