A biosensor is constituted by disposing an electrode system including a working electrode and a counter electrode on a substrate, forming an inorganic particulate-containing layer containing inorganic particulates thereon, and forming a reagent layer containing a reagent thereon. The inorganic particulates make it possible to prevent impurities in a sample from being in contact with the electrode system and being adsorbed therein, so that measurement is performed with high precision. The inorganic particulate-containing layer can be formed by applying a dispersion system of inorganic particulates and drying them, and it is preferable that the inorganic particulates are contained in the form of aggregates.