Real-time and label-free detection of antibodies from avian influenza (anti-Al) in an aqueous solution is demonstrated with the use of a nanowire field effect transistor. A real-time measurement system is constructed without leakage paths through the solution medium. The current through the nanowire changes significantly after an injection of an anti-Al solution onto the device, which was previously functionalized by the antigen of Al as a probe of anti-Al. In contrast, no significant response arises when an anti-Al solution is injected onto a non-functionalized device. Therefore, the real-time detection of specific antibody-antigen interaction of the Al is successfully implemented for a chip-based biosensor.