The release behavior of substrates encapsulated in the vesicle can be controlled by the interaction between the vesicular membrane and the protein. However, its control mechanism is still now unknown. Therefore, the protein-vesicle interaction was investigated by a pi-A isotherm. It was clarified that the released amount of encapsulated substrates increased with increasing protein-vesicle interaction. This result leads to the development of drug delivery systems (DDS) and of biosensor technology.