It is an object of the present invention to provide a sensor, which is capable of measuring, quickly and in high accuracy, concentration of neutral fat from a sample such as a biological sample or the like, without executing pretreatment of the sample. This object is attained by a biosensor for measuring concentration of neutral fat, based on value of current flowing in the electrode system, having: an insulating substrate; an electrode system having a working electrode and a counter electrode, formed onto the insulating substrate: and a reaction layer having a lipoprotein lipase, a glycerol dehydrogenase and an electron mediator, formed at the upper part or the vicinity of the electrode system.