This research paper has as its main purpose to compare diachronically the electoral law of Mexico State between 1978 and 2012, which has ruled the different elections of governor, members of the local congress and municipalities of this Mexican federal entity. From this analysis, we demonstrate that the enactment of the Electoral Code of Mexico State in 1996 expresses a profound change in the democratic quality of the electoral law of Mexico State, since it sets up norms that assure qualitatively superior levels of neatness and fairness than those achieved through the Act of Political Organizations and Electoral Procedures of Mexico State, which was enforced between 1978 and 1996.