CEOI 2025 warmly welcomes all participants to the competition and wishes them the best of luck, as follows:
Austria
| First Name | Last Name | Country | |
| Team Leader | Daniel | Fendrich | Austria |
| Deputy Leader | Florian | Siebenförcher | Austria |
| Contestant | Julian | Mejatsch | Austria |
| Contestant | Manuel | Zöttl | Austria |
| Contestant | Ben | Kinigadner | Austria |
| Contestant | Tom | Koska | Austria |
Bulgaria
| First Name | Last Name | Country | |
| Team Leader | Iliyan | Yordanov | Bulgaria |
| Deputy Leader | Encho | Mishinev | Bulgaria |
| Contestant | Boris | Mihov | Bulgaria |
| Contestant | Aleksandar | Gatev | Bulgaria |
| Contestant | Daniel | Koynov | Bulgaria |
| Contestant | Petar | Mihov | Bulgaria |
Croatia
| First Name | Last Name | Country | |
| Team Leader | Krešimir | Malnar | Croatia |
| Deputy Leader | Toni | Brajko | Croatia |
| Contestant | Dino | Hadžić | Croatia |
| Contestant | Fran | Škarica | Croatia |
| Contestant | Lovro | Tunjić | Croatia |
| Contestant | Nikola | Vujica | Croatia |
Czechia
| First Name | Last Name | Country | |
| Team Leader | Jiří | Kalvoda | Czechia |
| Deputy Leader | Benjamin | Swart | Czechia |
| Contestant | Adam | Houdek | Czechia |
| Contestant | Jan | Václavek | Czechia |
| Contestant | Petr | Starý | Czechia |
| Contestant | Hugo | Herynek | Czechia |
Georgia
| First Name | Last Name | Country | |
| Team Leader | Davit | Khvedelidze | Georgia |
| Deputy Leader | Giorgi | Kobakhia | Georgia |
| Contestant | Nikoloz | Melikishvili | Georgia |
| Contestant | Saba | Peradze | Georgia |
| Contestant | Vladimeri | Prangishvili | Georgia |
| Contestant | Davit | Dzadzamia | Georgia |
Germany
| First Name | Last Name | Country | |
| Team Leader | Erik | Sünderhauf | Germany |
| Deputy Leader | Julian | Baldus | Germany |
| Contestant | Maksym | Shvedchenko | Germany |
| Contestant | Shuheng | Wei | Germany |
| Contestant | Daphne | Carmesin | Germany |
| Contestant | Kevin Haocheng | Gong | Germany |
Hungary
| First Name | Last Name | Country | |
| Team Leader | Péter | Csorba | Hungary |
| Deputy Leader | Júlia | Éles | Hungary |
| Contestant | Tamás | Görömbey | Hungary |
| Contestant | Zsolt | Mihály | Hungary |
| Contestant | Gergely Péter | Sánta | Hungary |
| Contestant | Balázs | Szilágyi | Hungary |
Moldova
| First Name | Last Name | Country | |
| Team Leader | Sergiu | Corlat | Moldova |
| Deputy Leader | Timur | Degteari | Moldova |
| Contestant | Alexandr | Sozîchin | Moldova |
| Contestant | Alexei | Baca | Moldova |
| Contestant | Dan | Sandu | Moldova |
Poland
| First Name | Last Name | Country | |
| Team Leader | Krzysztof | Stencel | Poland |
| Deputy Leader | Antoni | Buraczewski | Poland |
| Contestant | Franciszek | Szymula | Poland |
| Contestant | Jerzy | Olkowski | Poland |
| Contestant | Artur | Smoleński | Poland |
| Contestant | Kacper | Jonak | Poland |
Romania 1
| First Name | Last Name | Country | |
| Team Leader | Casian | Pătrășcanu | Romania 1 |
| Contestant | Rareș-Andrei | Neculau | Romania 1 |
| Contestant | Rareș-Felix | Tudose | Romania 1 |
| Contestant | Iulian-George | Arsenoiu | Romania 1 |
| Contestant | Luca-Mihai | Ilie | Romania 1 |
| Contestant unoff | Mihai-Valeriu | Voicu | Romania 1 |
Romania 2
| First Name | Last Name | Country | |
| Team Leader | Claudiu-Cristian | Gorea-Zamfir | Romania 2 |
| Contestant | Roland | Petrean | Romania 2 |
| Contestant | Andrei Paul | Iorgulescu | Romania 2 |
| Contestant | Luca-Valentin | Mureșan | Romania 2 |
| Contestant | Tudor Ștefan | Mușat | Romania 2 |
| Contestant unoff | Mircea Maxim | Rebengiuc | Romania 2 |
Serbia
| First Name | Last Name | Country | |
| Team Leader | Dragan | Urošević | Serbia |
| Deputy Leader | Nemanja | Majski | Serbia |
| Contestant | Uroš | Kostadinović | Serbia |
| Contestant | Sofija | Čebašek | Serbia |
| Contestant | Dimitrije | Atanasković | Serbia |
| Contestant | Filip | Repman | Serbia |
Slovakia
| First Name | Last Name | Country | |
| Team Leader | Jozef | Číž | Slovakia |
| Deputy Leader | Truc Lam | Bui | Slovakia |
| Contestant | Hana | Kalábová | Slovakia |
| Contestant | Viliam | Gottweis | Slovakia |
| Contestant | Norbert | Barnáš | Slovakia |
| Contestant | Ján | Sliacky | Slovakia |
Slovenia
| First Name | Last Name | Country | |
| Team Leader | Jan | Berčič | Slovenia |
| Deputy Leader | Patrik | Žnidaršič | Slovenia |
| Contestant | Luka | Heric | Slovenia |
| Contestant | Jakob | Omahen | Slovenia |
| Contestant | Rok | Lavrič | Slovenia |
| Contestant | Mitja | Ševerkar | Slovenia |
Switzerland
| First Name | Last Name | Country | |
| Team Leader | Johannes | Kapfhammer | Switzerland |
| Deputy Leader | Cheng | Zhong | Switzerland |
| Contestant | Yuhua | Su | Switzerland |
| Contestant | Jonathan | Braun | Switzerland |
| Contestant | Myriam | Faltin | Switzerland |
| Contestant | Zeno | Orglmeister | Switzerland |
Ukraine
| First Name | Last Name | Country | |
| Team Leader | Oleksandr | Mitsa | Ukraine |
| Deputy Leader | Kostiantyn | Denysov | Ukraine |
| Contestant | Valerii | Kovnatskyi | Ukraine |
| Contestant | Illia | Shevchenko | Ukraine |
| Contestant | Daria | Perekopska | Ukraine |
| Contestant | Stepan | Simak | Ukraine |