Following are contestants of the 16th IOAA:

Afghanistan
Armenia
Austria
Azerbaijan
Bangladesh
Brazil
Bulgaria
Canada
China
Colombia
Croatia
Cyprus
Czechia
Ecuador
El Salvador
Estonia
France
Georgia
Germany
Greece
Hungary
India
Indonesia
Iran
Japan
Kazakhstan
Kyrgyzstan
Latvia
Lithuania
Malaysia
Nepal
Norway
Pakistan
Peru
Philippines
Poland
Portugal
Romania
Saudi Arabia
Serbia
Singapore
Slovakia
Slovenia
South Korea
Sri Lanka
Sweden
Thailand
Türkiye
Ukraine
United Arab Emirates
United Kingdom
United States of America
Vietnam