When Is UN Day Celebrated? is a useful question for students, educators, and anyone interested in international observances. United Nations Day is celebrated every year on 24 October, commemorating the date when the United Nations Charter came into force in 1945.UN Day highlights the importance of international cooperation, peace, human rights, humanitarian support, and sustainable development. Schools, organizations, governments, and communities around the world observe the occasion through educational programs, awareness campaigns, discussions, cultural activities, and other initiatives.