| Season: | 2005 |
| Competition: | Samsung Hauzen K League |
| Winners: | Ulsan Hyundai Horang-i (2nd title) |
| Continentalcup1: | Champions League |
| Continentalcup1 Qualifiers: | Ulsan Hyundai Horang-i Jeonbuk Hyundai Motors |
| Matches: | 156 |
| Total Goals: | 373 |
| Best Player: | Lee Chun-soo |
| League Topscorer: | Leandro Machado (13 goals) |
| Prevseason: | 2004 |
| Nextseason: | 2006 |
The 2005 K League was the 23rd season of the K League. It kicked off on May 15, and was finished on 4 December. The format of the regular season and championship playoffs was the same as the one used in the 2004 season.
Busan IPark won the first stage, and the second stage was won by Seongnam Ilhwa Chunma. Two winners were guaranteed their slot in the end-of-season playoffs. Incheon United and Ulsan Hyundai Horang-i also joined the playoffs according to the overall table after two stages. In the semi-finals Ulsan defeated Seongnam 2–1, and Incheon defeated Busan 2–0. The two victorious teams faced each other in the two-legged championship final. Ulsan won the first leg 5–1 at the Incheon stadium, and though Incheon won the second leg 2–1, Ulsan lifted their second league title 6–3 on aggregate.
The first place team qualified for the championship playoffs.
The first place team qualified for the championship playoffs.
The top two teams in the overall table qualified for the championship playoffs.
See main article: 2005 K League Championship.
This list includes goals of the championship playoffs.
| Rank | Player | Club | Goals | Apps |
|---|---|---|---|---|
| 1 |  Leandro Machado | Ulsan Hyundai Horang-i | 13 | 17 |
| 2 | Park Chu-young | FC Seoul | 12 | 19 |
| 3 | Dudu | Seongnam Ilhwa Chunma | 10 | 24 |
| Sandro Hiroshi | Daegu FC | 10 | 24 | |
| 5 | Kim Do-hoon | Seongnam Ilhwa Chunma | 9 | 20 |
| Dženan Radončić | Incheon United | 9 | 22 | |
| Luciano Valente | Busan IPark | 9 | 22 | |
| Da Silva | Pohang Steelers | 9 | 24 | |
| 9 | Mota | Seongnam Ilhwa Chunma | 7 | 9 |
| Lee Chun-soo | Ulsan Hyundai Horang-i | 7 | 14 | |
 Adrian Neaga | Jeonnam Dragons | 7 | 15 | |
| Leandrão | Daejeon Citizen | 7 | 19 | |
| Nam Ki-il | Seongnam Ilhwa Chunma | 7 | 20 | |
| Kim Eun-jung | FC Seoul | 7 | 20 | |
| Selmir | Incheon United | 7 | 25 |
| Award | Winner | Club | |
|---|---|---|---|
| Most Valuable Player |  Lee Chun-soo | Ulsan Hyundai Horang-i | |
| Top goalscorer[1] | Leandro Machado | Ulsan Hyundai Horang-i | |
| Top assist provider | Ricardo Nascimento | Daegu FC | |
| Rookie of the Year | Park Chu-young | FC Seoul | |
| Manager of the Year | Chang Woe-ryong | Incheon United |
| Position | Winner | Club |
|---|---|---|
| Goalkeeper | Kim Byung-ji | Pohang Steelers |
| Defenders | Lim Joong-yong | Incheon United |
| Yoo Kyoung-youl | Ulsan Hyundai Horang-i | |
| Cho Yong-hyung | Bucheon SK | |
| Kim Young-chul | Seongnam Ilhwa Chunma | |
| Midfielders | Lee Chun-soo | Ulsan Hyundai Horang-i |
| Lee Ho | Ulsan Hyundai Horang-i | |
| Kim Do-heon | Seongnam Ilhwa Chunma | |
| Cho Won-hee | Suwon Samsung Bluewings | |
| Forwards | Park Chu-young | FC Seoul |
| Leandro Machado | Ulsan Hyundai Horang-i |