| Election Name: | 1966 United States Senate election in South Dakota |
| Country: | South Dakota |
| Flag Year: | 1963 |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1960 United States Senate election in South Dakota |
| Previous Year: | 1960 |
| Next Election: | 1972 United States Senate election in South Dakota |
| Next Year: | 1972 |
| Election Date: | November 8, 1966 |
| Image1: | File:Rep. Karl Mundt, Repub., of S.D., 2-21-40 LCCN2016877155 (cropped).jpg |
| Nominee1: | Karl Mundt |
| Party1: | Republican Party (United States) |
| Popular Vote1: | 150,517 |
| Percentage1: | 66.28% |
| Nominee2: | Donn H. Wright |
| Party2: | Democratic Party (United States) |
| Popular Vote2: | 76,563 |
| Percentage2: | 33.72% |
| Map Size: | 260px |
| U.S. Senator | |
| Before Election: | Karl E. Mundt |
| Before Party: | Republican Party (United States) |
| After Election: | Karl E. Mundt |
| After Party: | Republican Party (United States) |
The 1966 United States Senate election in South Dakota took place on November 8, 1966. Incumbent Republican Senator Karl E. Mundt ran for re-election to his fourth term. He was challenged in the Republican primary by a John Birch Society member, but easily turned away the challenge. In the general election, he faced State Representative Donn Wright, the Democratic nominee. Owing in large part to the Republican landslide taking place nationwide, Mundt defeated Wright by an unprecedented margin.
State Representative Donn Wright from Aurora County announced that he would run against Mundt on April 18, 1966, the only Democratic candidate to do so.[1] As Wright was the only candidate to file for the nomination, he won the primary unopposed and the race was removed from the primary election ballot.[2]