| Event: | Men's 800 metre freestyle |
| Competition: | 2009 FINA World Championships |
| Venue: | Foro Italico |
| Dates: | 28 July 2009 (heats, semifinals) 29 July 2009 (final) |
| Competitors: | 56 |
| Nations: | 40 |
| Win Value: | 7:32.12 |
| Gold: | Zhang Lin |
| Goldnoc: | CHN |
| Silver: | Oussama Mellouli |
| Silvernoc: | TUN |
| Bronze: | Ryan Cochrane |
| Bronzenoc: | CAN |
| Prev: | 2007 |
| Next: | 2011 |
See main article: Swimming at the 2009 World Aquatics Championships.
The men's 800 metre freestyle at the 2009 World Championships occurred on the morning of Tuesday, 28 July (heats) and the evening Wednesday 29 July (final) at the Foro Italico in Rome, Italy.
| World record | 7:38.65 | Montreal, Canada | align=right | 27 July 2005 | ||
| Championship record | 7:38.65 | Montreal, Canada | align=right | 27 July 2005 |
The following records were established during the competition:
| Rank | Name | Nationality | Time | Heat | Lane | Notes | |
|---|---|---|---|---|---|---|---|
| 1 | 7:41.82 | 6 | 5 | AF | |||
| 2 | 7:43.61 | 6 | 4 | AM | |||
| 3 | 7:44.29 | 4 | 3 | ER | |||
| 4 | 7:45.89 | 4 | 5 | NR | |||
| 5 | 7:46.05 | 5 | 4 | NR | |||
| 6 | 7:48.75 | 6 | 3 | ||||
| 7 | 7:49.09 | 6 | 6 | NR | |||
| 8 | 7:49.71 | 5 | 6 | ||||
| 9 | 7:50.10 | 5 | 5 | ||||
| 10 | 7:50.65 | 4 | 6 | ||||
| 11 | 7:52.18 | 6 | 7 | NR | |||
| 12 | 7:53.92 | 5 | 2 | ||||
| 13 | 7:55.43 | 4 | 0 | ||||
| 14 | 7:57.09 | 5 | 8 | ||||
| 15 | 7:59.16 | 6 | 1 | ||||
| 16 | 7:59.67 | 4 | 4 | ||||
| 17 | 8:00.50 | 5 | 1 | ||||
| 18 | 8:01.50 | 6 | 2 | ||||
| 19 | 8:02.35 | 5 | 7 | ||||
| 20 | 8:03.27 | 4 | 1 | NR | |||
| 21 | 8:05.12 | 4 | 8 | ||||
| 22 | 8:05.68 | 3 | 3 | ||||
| 23 | 8:08.64 | 3 | 5 | ||||
| 24 | 8:09.16 | 6 | 8 | ||||
| 25 | 8:10.26 | 1 | 1 | ||||
| 26 | Fabio Pereira | 8:11.60 | 5 | 0 | |||
| 27 | 8:11.79 | 4 | 2 | ||||
| 28 | 8:12.36 | 1 | 2 | ||||
| 29 | 8:13.16 | 3 | 2 | ||||
| 30 | 8:14.67 | 6 | 9 | ||||
| 31 | 8:16.93 | 1 | 7 | ||||
| 32 | 8:20.55 | 3 | 7 | ||||
| 33 | 8:20.94 | 5 | 9 | ||||
| 34 | 8:22.12 | 3 | 4 | ||||
| 35 | 8:25.81 | 6 | 0 | ||||
| 36 | 8:29.57 | 4 | 9 | ||||
| 37 | 8:33.44 | 3 | 8 | ||||
| 38 | 8:35.57 | 2 | 9 | ||||
| 39 | 8:36.04 | 3 | 1 | ||||
| 40 | 8:39.69 | 2 | 3 | ||||
| 41 | 8:43.89 | 3 | 0 | ||||
| 42 | 8:44.09 | 2 | 5 | ||||
| 43 | 8:45.18 | 2 | 7 | ||||
| 44 | 8:54.03 | 3 | 9 | ||||
| 45 | 8:54.06 | 2 | 6 | ||||
| 46 | 8:55.64 | 2 | 1 | NR | |||
| 47 | 8:56.92 | 2 | 2 | ||||
| 48 | 8:59.14 | 2 | 8 | ||||
| 49 | 8:59.58 | 2 | 0 | ||||
| 50 | 9:11.37 | 1 | 4 | ||||
| 51 | 9:38.96 | 1 | 3 | ||||
| 52 | 9:40.57 | 1 | 5 | ||||
| – | DNS | 1 | 6 | ||||
| – | DNS | 2 | 4 | ||||
| – | DNS | 4 | 7 | ||||
| – | DNS | 5 | 3 |
| Rank | Name | Nationality | Time | Lane | Notes | |
|---|---|---|---|---|---|---|
| 7:32.12 | 7 | WR | ||||
| 7:35.27 | 4 | AF | ||||
| 7:41.92 | 5 | AM | ||||
| 4 | 7:43.84 | 3 | ER | |||
| 5 | 7:44.32 | 6 | NR | |||
| 6 | 7:48.44 | 8 | ||||
| 7 | 7:49.46 | 1 | ||||
| 7 | 7:49.46 | 2 |