main objective of the research whose results are presented here consisted I n analyzing the legal basis and implications that the principle of proportionality applied in the judicial imposition of penalty has. methodology used required attesting the next steps: It started from the doctoral thesis The principle of proportionality and the criminal law by Lopera Mesa (2006), which explores the possibility of using this principle in the abstract constitutional control of criminal laws. To determine the constitutional and legal basis, which enable the use of the principle of proportionality to the concrete case of Colombia, documentary sources were used such as doctrine, rules and jurisprudence. Some cases were developed to assess the proportionality in sentencing, establishing in consequence the implications and limitations of such a task. main conclusion is: judges have the constitutional and legal obligation (articles 3, 59 and 13 CP) to move off from laws related to the penalty when they originate a disproportionate effect on fundamental rights. This reaffirms the principle of legality, in its simple and strict sense, rather than attempting against it. Furthermore, the regulation (article 6 CP) of the analogy in bonampartem supports this idea.