This is a list of songs which reached number one on the Billboard Mainstream Top 40 chart in 2004.
During 2004, a total of 12 singles hit number-one on the charts.
| Issue date | Song | Artist(s) | Ref. |
|---|---|---|---|
| January 3 | "Hey Ya!" | OutKast | [1] |
| January 10 | |||
| January 17 | |||
| January 24 | |||
| January 31 | |||
| February 7 | |||
| February 14 | "The Way You Move" | OutKast featuring Sleepy Brown | |
| February 21 | |||
| February 28 | |||
| March 6 | "With You" | Jessica Simpson | |
| March 13 | |||
| March 20 | "Toxic" | Britney Spears | |
| March 27 | |||
| April 3 | |||
| April 10 | |||
| April 17 | "Yeah!" | Usher featuring Lil Jon and Ludacris | |
| April 24 | |||
| May 1 | |||
| May 8 | "This Love" | Maroon 5 | |
| May 15 | |||
| May 22 | |||
| May 29 | "The Reason" | Hoobastank | |
| June 5 | |||
| June 12 | |||
| June 19 | |||
| June 26 | |||
| July 3 | |||
| July 10 | |||
| July 17 | |||
| July 24 | "Leave (Get Out)" | JoJo | |
| July 31 | |||
| August 7 | |||
| August 14 | |||
| August 21 | |||
| August 28 | "Pieces of Me" | Ashlee Simpson | |
| September 4 | |||
| September 11 | |||
| September 18 | |||
| September 25 | |||
| October 2 | "She Will Be Loved" | Maroon 5 | |
| October 9 | |||
| October 16 | "My Happy Ending" | Avril Lavigne | |
| October 23 | "She Will Be Loved" | Maroon 5 | |
| October 30 | |||
| November 6 | "Over and Over" | Nelly featuring Tim McGraw | |
| November 13 | |||
| November 20 | |||
| November 27 | |||
| December 4 | |||
| December 11 | |||
| December 18 | |||
| December 25 |