In this paper we discuss the reason for the widely found discrepancy between Sérsic brightness law fitted along major and minor axes of elliptical galaxies. We show that this difference is a natural consequence of the isophotes eccentricity law. We present a mathematical transformation that allows to obtain the minor axis Sérsic's law from that of the mayor axis one, provided that the eccentricity can be represented by a well behaved, though very general, function of the radius, and that the isophotes ellipses major axis are aligned and concentric. For constant eccentricity, only the coefficient of R1/n is changed, while for distance dependent eccentricity the transformation is given by the Lerch F transcendental function. We discuss 28 galaxies of type E0 to E7, dS0 and S0.