It is an object of the present invention to provide a method for carrying out on a same biosensor both of the measurement of the amount of a physiologically active substance immobilized on a biosensor substrate and the measurement of the biological activity of the above physiologically active substance, thereby analyzing the interaction of a substance with the above physiologically active substance that maintains its activity. The present invention provides a measurement method using a biosensor substrate, wherein both the amount of a physiologically active substance immobilized on the substrate and the biological activity of the physiologically active substance immobilized on the substrate are measured on said same biosensor substrate.