Bio-related reactions are broadly applicable in detection and determination of specific substances as well as in chemical synthesis. Many types of biosensors have been developed by use of biomaterials, such as enzymes, antibodies and binding proteins. In biosensing systems, it is essential to convert chemical and/or physical changes accompanying specific molecular recognition with the biomaterials into definite information. Bioelectrochemical systems consisting of biochemical and electrochemical reactions are promising candidates to inform the biochemical molecular recognition as electrical signals. In this article are surveyed the molecular recognition with biomaterials, their application to biosensors, especially to bioelectrochemical sensors, and the example of amperometric sensing with them.