| Election Name: | 1986 United States Senate election in South Dakota |
| Country: | South Dakota |
| Flag Year: | 1963 |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1980 United States Senate election in South Dakota |
| Previous Year: | 1980 |
| Next Election: | 1992 United States Senate election in South Dakota |
| Next Year: | 1992 |
| Election Date: | November 4, 1986 |
| Image1: | TomDaschlePortrait (1).jpg |
| Nominee1: | Tom Daschle |
| Party1: | Democratic Party (United States) |
| Popular Vote1: | 152,657 |
| Percentage1: | 51.60% |
| Nominee2: | James Abdnor |
| Party2: | Republican Party (United States) |
| Popular Vote2: | 143,173 |
| Percentage2: | 48.40% |
| Map Size: | 260px |
| U.S. Senator | |
| Before Election: | James Abdnor |
| Before Party: | Republican Party (United States) |
| After Election: | Tom Daschle |
| After Party: | Democratic Party (United States) |
The 1986 United States Senate election in South Dakota was held on November 4, 1986. Incumbent Republican U.S. Senator James Abdnor ran for re-election to a second term, but was defeated by Democrat and future Senate Majority Leader Tom Daschle.[1] This election was the only United States Senate election in South Dakota that Daschle would win by a narrow margin.
Although Abdnor won the primary by a fairly comfortable margin, it hurt him badly. Daschle was uncontested for the Democratic nomination and therefore was able to focus on the general election early, while Abdnor had to fight a challenge from a popular incumbent governor. Many political analysts say this was one of the factors in Abdnor's general election loss.