The present invention provides a method of measuring a component in blood, by which an amount of the component can be corrected accurately by measuring a hematocrit (Hct) value of the blood with high accuracy and high reliability and also provides a sensor used in the method. The method of measuring a component in blood using a biosensor comprising a first electrode system including a first working electrode on which at least an oxidoreductase that acts upon the component and a mediator are provided and a first counter electrode and a second working electrode on which the mediator is not provided. The first working electrode and the first counter electrode are used for obtaining the amount of the component and the second working electrode and the first working electrode are used for obtaining the amount of the blood cells.