| Election Name: | 1918 United States Senate special election in Missouri |
| Country: | Missouri |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1914 United States Senate election in Missouri |
| Previous Year: | 1914 |
| Next Election: | 1920 United States Senate election in Missouri |
| Next Year: | 1920 |
| Image1: | Selden Palmer Spencer.jpg |
| Nominee1: | Selden P. Spencer |
| Party1: | Republican Party (US) |
| Popular Vote1: | 302,680 |
| Percentage1: | 52.39% |
| Nominee2: | Joseph W. Folk |
| Party2: | Democratic Party (US) |
| Popular Vote2: | 267,397 |
| Percentage2: | 46.29% |
| Map Size: | 270px |
| U.S. senator | |
| Before Election: | Xenophon P. Wilfley |
| Before Party: | Democratic Party (US) |
| After Election: | Selden P. Spencer |
| After Party: | Republican Party (US) |
The 1918 United States Senate special election in Missouri took place on November 5, 1918 in Missouri. Democrat William J. Stone was elected to the full term in 1914, but died on April 14, 1918. Xenophon P. Wilfley was appointed to the vacant seat on April 30, 1918. He lost the Democratic primary election to Joseph W. Folk, who was defeated by Republican Selden P. Spencer in the general election.