The steady electrophoretic mobility of a spherical colloidal particle carrying low zeta potential in an electrolyte solution under an applied constant electric field is described with the Henry function. When a step electric field is applied to a spherical colloidal particle, the Henry function should be modified so as to be time-dependent. Huang and Keh presented a rigorous theory of the transient unsteady electrophoresis of a spherical particle. In a previous paper we have derived a simple analytic approximate expression for the time-dependent transient Henry function. The present paper reviews a study of the time-dependent transient Henry function.