| Election Name: | 1918 United States Senate election in Montana |
| Country: | Montana |
| Flag Year: | 1905 |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1912 United States Senate election in Montana |
| Previous Year: | 1912 |
| Next Election: | 1924 United States Senate election in Montana |
| Next Year: | 1924 |
| Election Date: | November 5, 1918 |
| Image1: | Thomas J. Walsh cph.3c02581.jpg |
| Nominee1: | Thomas J. Walsh |
| Party1: | Democratic Party (United States) |
| Popular Vote1: | 46,160 |
| Percentage1: | 41.07% |
| Nominee2: | Oscar M. Lanstrum |
| Party2: | Republican Party (United States) |
| Popular Vote2: | 40,229 |
| Percentage2: | 35.79% |
| Image3: | Jeannette Rankin cph.3b13863.jpg |
| Nominee3: | Jeannette Rankin |
| Party3: | National Party (United States) |
| Popular Vote3: | 26,013 |
| Percentage3: | 23.14% |
| Map Size: | 300px |
| U.S. Senator | |
| Before Election: | Thomas J. Walsh |
| Before Party: | Democratic Party (United States) |
| After Election: | Thomas J. Walsh |
| After Party: | Democratic Party (United States) |
The 1918 United States Senate election in Montana took place on November 5, 1918. Incumbent United States Senator Thomas J. Walsh, who was first elected to the Senate in 1912, ran for re-election. He won the Democratic primary uncontested, and was opposed in the general election by Oscar M. Lanstrum, a former State Representative and the Republican nominee, and Jeannette Rankin, one of two United States representatives from Montana's at-large congressional district and the nominee of the National Party. Walsh narrowly won his second term in the Senate.