A method for determining boundary points in electrophoresis comprising a step to determine points on the abscissa corresponding to peak tops on a densitogram traced on the basis of electrophoresis of a standard sample as standard positions, a step to locate positions corresponding to said standard positions on a densitogram traced on the basis of electrophoresis of an unknown sample, a step to determine the point corresponding to the lowest concentration among points having minimum values between each pair of neighboring standard positions as the normal boundary point and a step to calculate an integral or a value proportional to the integral of each fraction delimited by the boundary points thus determined.