Jurnal Cita Hukum. Faculty of Sharia and Law UIN Jakarta Vol. 5 No. 2 (2017), pp.211-232, DOI: 10.15408/jch.v5i2.4959 ------------------------------------------------------------------------------------ 211 The Principle of Legality in Criminal Act of Terrorism  Hariman Satria Faculty of Law, University of Muhammadiyah Kendari Jl. KH Ahmad Dahlan Nomor 10 Kendari E-mail: hariman85antikorupsi@gmail.com DOI: 10.15408/jch.v5i2.4959 Abstract The trial of Imam Samudera cs uses Perppu No 1 2002 on Combating Criminal Acts of Terrorism. This regulation was made after Bali bombing 1. So the criminal provisions were made retroactively. Similarly, in cases of serious human rights violations in East Timor, the perpetrators use retroactive laws. Enforcement of the criminal provisions retroactively also made by the ad hoc international criminal court through Nurenberg Trial and Tokyo Trial in 1945. Enforcement of the criminal provisions aimed at fulfilling the principle of justice, that the convict by violating the principle of legality is not fair but not punishing guilty of serious crimes which did not fare much better. Strictly speaking, the principle of legality can be set aside. Keyword: Principle of Legality, Criminal Act, Terrorism  Received: June 14, 2017, Revised: July 12, 2017, Accepted: Agustus 22, 2017.