This  article examines  legal mechanisms  for countering  terrorism within  the system  of regional  international organizations.  It analyzes  the regulatory  frameworks and  institutional foundations  of such  organizations as  the Council  of Europe,  the Shanghai  Cooperation Organization,  the Organization  for Security  and Co-operation in  Europe, and  others in  the field  of combating  terrorist activities.  Particular attention  is paid  to the  coordination of  efforts among  member states,  the unification  of legal  approaches, and  the development  and implementation  of joint  measures aimed  at preventing  and suppressing  terrorism. The  study also  explores the  specific features  of regional  cooperation, including  information exchange,  joint operations,  and the  harmonization of  national legislation.  Current challenges  related to  differences in  legal systems,  the level  of interstate  interaction, and  the effectiveness  of implementation  of adopted  decisions are  identified. The  conclusion outlines  the main  directions for  improving legal  mechanisms for  countering terrorism  within regional  international organizations.