The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization, or CTBTO Preparatory Commission is an international organization based in Vienna, Austria, that is tasked with building up the verification regime of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The organization was established by the States Signatories to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in 1996.

Its main purpose is twofold: to promote the entry into force of the CTBT, and to establish a global verification regime in preparation for the Treaty's entry into force.

As the CTBTO Preparatory Commission is an interim organization, it will be dissolved once the CTBT enters into force and will be replaced by the CTBTO, with all its assets being transferred to the CTBTO. This change will occur at the close of the first Conference of States Parties of the CTBT, which will take place when the Treaty has entered into force. For the Treaty to enter into force, the following states need to ratify the CTBT: China, Democratic People's Republic of Korea, Egypt, India, Iran (Islamic republic of), Israel, Pakistan and the United States of America. Entry into force will occur 180 days after these states ratify the Treaty.