This work proposes to review the use of the principle of proportionality in the decisions of the Constitutional Courts of Chile and Colombia dealing with judicial review of criminal law. The purpose of the work is to investigate how such a tool has contributed to the function of increasing the rationality in the control of criminal political decisions of the legislative branch. To do so, the work first examines the differences between the constitutional justice systems. On this basis, it is ascertained whether, to what extent and on what occasions these constitutional courts have asked the questions and incorporated the demands that the proportionality principle as an argumentative tool in the judicial review of substantive criminal law requires.