The single nation that owns the most aircraft carriers is the United Kingdom, which has 41 aircraft carriers (2 of them are under construction). However, the United States of America own 66 aircraft carriers (2 of them are also under construction).
USA: 66 aircraft carriers
UK: 41 aircraft carriers
Japan: 31 aircraft carriers
France: 26 aircraft carriers
Germany: 23 aircraft carriers
Russia: 9 aircraft carriers
Italy: 6 aircraft carriers
Canada: 5 aircraft carriers
Australia, Spain and India: 4 aircraft carriers
Brazil, Argentina and Netherlands: 2 aircraft carriers
Thailand and Ukraine: 1 aircraft carrier