| Election Name: | 1866 Pennsylvania gubernatorial election |
| Country: | Pennsylvania |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1863 Pennsylvania gubernatorial election |
| Previous Year: | 1863 |
| Next Election: | 1869 Pennsylvania gubernatorial election |
| Next Year: | 1869 |
| Party1: | Republican Party (United States) |
| Nominee1: | John W. Geary |
| Popular Vote1: | 307,274 |
| Percentage1: | 51.4% |
| Nominee2: | Hiester Clymer |
| Party2: | Democratic Party (United States) |
| Popular Vote2: | 290,096 |
| Percentage2: | 48.6% |
| Map Size: | 250px |
| Governor | |
| Before Election: | Andrew Gregg Curtin |
| Before Party: | Republican Party (United States) |
| After Election: | John W. Geary |
| After Party: | Republican Party (United States) |
The 1866 Pennsylvania gubernatorial election occurred on October 9, 1866. Incumbent governor Andrew Gregg Curtin, a Republican, was not running for re-election.
Republican candidate John W. Geary defeated Democratic candidate Hiester Clymer to become Governor of Pennsylvania.