The theory of cyclic voltammetry for a quasi-reversible reaction at a hemispherical microelectrode has been deduced. From the results calculated according to the theory, the heterogeneous rate constant and charge transfer coefficient can be measured with the cyclic voltammetric data obtained at an intermediate scan rate on a hemispherical microelectrode. To verify the theory, the kinetic constant for reduction of benzoquinone in acetonitrile has been determined. The result is coincident with that measured by a fast scan rate at a platinum microdisk electrode. The kinetic constant and charge transfer coefficient for reduction of 2,3,5,6-tetrachlorobenzoquinone have also been determined with the method described in this paper.