| Election Name: | 2004 United States Senate election in Iowa |
| Country: | Iowa |
| Flag Image: | Flag of Iowa (xrmap collection).svg |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1998 United States Senate election in Iowa |
| Previous Year: | 1998 |
| Next Election: | 2010 United States Senate election in Iowa |
| Next Year: | 2010 |
| Election Date: | November 2, 2004 |
| Image1: | Chuck Grassley official photo.jpg |
| Nominee1: | Chuck Grassley |
| Party1: | Republican Party (United States) |
| Popular Vote1: | 1,038,175 |
| Percentage1: | 70.18% |
| Nominee2: | Arthur A. Small |
| Party2: | Democratic Party (United States) |
| Popular Vote2: | 412,365 |
| Percentage2: | 27.88% |
| Map Size: | 240px |
| U.S. Senator | |
| Before Election: | Chuck Grassley |
| Before Party: | Republican Party (United States) |
| After Election: | Chuck Grassley |
| After Party: | Republican Party (United States) |
The 2004 United States Senate election in Iowa was held on November 2, 2004. Incumbent Republican United States Senator Chuck Grassley ran for re-election to a fifth term in the United States Senate. Grassley and former State Senator Arthur A. Small won the Republican and Democratic primaries, respectively, unopposed, and faced each other in the general election. Though this election coincided with the highly competitive presidential election, Grassley was not considered vulnerable and defeated Small in a landslide.
As of, this is the last time a Republican Senate candidate won Johnson County. As of 2024, this is also the last time that the winning United States Senate candidate carried all counties in Iowa for this seat.