This invention relates to a biosensor which comprises an insulative base, an electrode system formed on the substrate and primarily made of carbon, and a perforated body having an enzyme and an electron acceptor and integrally combined with the electrode system whereby a concentration of a specific component in a biological liquid sample can be electrochemically measured rapidly and accurately by a simple procedure of mere addition of the liquid sample. Several simple biosensors for measuring a specific component in a liquid sample are known including a sensor of the type in which a change of a dye formed by an enzyme reaction is optically detected and a sensor of the type using an enzyme electrode. These sensors, respectively, involve an interference with colored matters in liquid sample and necessity of washing of an electrode system every measuring procedure. In addition, the sensors are complicated in structure and materials therefor are expensive. In the present invention, the electrode system is formed mainly of carbon and is integrally combined with the perforated body, so that washing of the electrode system is unnecessary. Thus, an inexpensive, simply-operated biosensor of the disposable type can be provided.