Making of the principle of legality in the context of the enactment of criminal law according to time, contain the issue of retroactive principle as an exception from the principle of lex tempor is delicti. This study aimed to analyze the policy retroactive enforcement of criminal law in the transitional period applicable in Ind onesia and perspective of comparative study of an tara Penal Code (WvS) with Concept RKUHP New. This study included doctrinal-research with spes ifikasinya descriptive-analytic ber approach to legislation which supported the comparative approach. The conclusion of this study shows that the nature of the retroactive application of criminal law in the transitional period in Indonesia is based on benchmarks/criteria, namely (1) there are changes in legislation and (2) there are mitigating rules for defendants. While the study of comparative turned out to show their conceptual development, initially in the Criminal Code criteria are limited to rules that relieve the defendant, pulling in Ko nsep New RKUHP is expanding benchmarks / criteria regarding legislative changes that relieve the defendant applies to convict.