| Participations | Number of | ||||
| first year | last year | participations | hosting | ||
| 1 | Armenia | 1997 | 2016 | 17 | - |
| 2 | Bangladesh | 2018 | 2019 | 2 | - |
| 3 | Belorussia | 2000 | 2008 | 3 | - |
| 4 | Bolivia | 2012 | 2012 | 1 | - |
| 5 | Brazil | 1998 | 2007 | 9 | - |
| 6 | Bulgaria | 1998 | 2019 | 22 | 1 |
| 7 | Canada | 2010 | 2010 | 1 | - |
| 8 | China | 2002 | 2019 | 17 | 3 |
| 9 | Crimea * | 1999 | 2013 | 7 | 5 |
| 10 | Croatia | 2007 | 2010 | 4 | - |
| 11 | Czechia | 2007 | 2019 | 12 | - |
| 12 | Estonia | 1991 | 2014 | 11 | - |
| 13 | Finland | 1996 | 1996 | 1 | - |
| 14 | India | 1997 | 2019 | 23 | 1 |
| 15 | Indonesia | 2003 | 2013 | 11 | - |
| 16 | Iran | 2003 | 2018 | 7 | - |
| 17 | Italy | 2001 | 2019 | 16 | 1 |
| 18 | Kazakhstan | 2006 | 2019 | 12 | 1 |
| 19 | Kirgizia | 2011 | 2016 | 3 | 1 |
| 20 | Korea | 2002 | 2019 | 18 | 1 |
| 21 | Latvia | 1990 | 1991 | 2 | - |
| 22 | Lithuania | 2003 | 2019 | 13 | 1 |
| 23 | Macedonia | 2016 | 2016 | 1 | - |
| 24 | Malaysia | 2019 | 2019 | 1 | - |
| 25 | Mongolia | 2012 | 2012 | 1 | - |
| 26 | Moscow Land * | 1990 | 2019 | 26 | 2 |
| 27 | Nepal | 2018 | 2019 | 2 | - |
| 28 | Pakistan | 2014 | 2018 | 2 | - |
| 29 | Romania | 2003 | 2019 | 17 | 1 |
| 30 | Russia | 1990 | 2019 | 26 | 6 |
| 31 | Serbia (incl. Yug, S&M) | 2002 | 2011 | 9 | - |
| 32 | Sri Lanka | 2012 | 2019 | 5 | 1 |
| 33 | Sweden | 1996 | 2019 | 17 | 1 |
| 34 | Thailand | 2004 | 2019 | 15 | - |
| 35 | Ukraine | 1999 | 2019 | 11 | - |
| 36 | USA | 2019 | 2019 | 1 | - |
| 37 | Vietnam | 2017 | 2019 | 3 | - |
(*) Moscow Land and Peninsula of Crimea, as organizers of the oldest open astronomical Olympiads/competitions (have existed for more than 50 years), and due to their historical service in the formation and development of IAO, they are considered as independent states with all rights and duties. Both Moscow Land and Crimea are geographical terms and have no any administrative or political meaning.