Biosensor for electrochemical measurement of 1,5-anhydroglucitol, and measuring method and measuring kit using the same

The biosensor has an electrode system for electrochemically measuring 1,5-anhydroglucitol (1,5-AG) and a reagent layer formed on said electrode system. The reagent layer contains an enzyme for measuring 1,5-anhydroglucitol, phenothiazine compounds, a stabilizer selected from a group of compounds comprising metal salts, organic acids, and amino acids, and an acidic polymer compound as an optional ingredient. The biosensor has excellent storage stability and can electrochemically measure 1,5-anhydroglucitol unaffected by the hematocrit contained in a whole blood sample.