Abstract: An object of the present invention is to provide a method and a kit that can accurately measure autoantibody activity against a TSH receptor in a short time without pretreating a blood sample (blood specimen). The autoantibody activity against a TSH receptor in a blood sample can be measured by using a kit for measurement of autoantibody activity against a TSH receptor in a mammal cell, comprising a mammal cell expressing both a cAMP biosensor and the TSH receptor, and a substrate capable of visualizing and/or quantifying the cAMP biosensor as constituents, and performing a method comprising the steps of: (a) incubating a mammal cell expressing both a cAMP biosensor and the TSH receptor in the presence of a blood sample collected from a test subject; (b) measuring an activation level of the cAMP biosensor after the step (a); and (c) comparing the activation level measured in the step (b) with an activation level in a control to calculate the autoantibody activity.