| Election Name: | 2009 San Antonio mayoral election |
| Flag Image: | Flag of San Antonio, Texas.svg |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 2007 San Antonio mayoral election |
| Previous Year: | 2007 |
| Next Election: | 2011 San Antonio mayoral election |
| Next Year: | 2011 |
| Election Date: | May 9, 2009 |
| Turnout: | 11.61% |
| Candidate1: | Julian Castro |
| Colour1: | c0c0c0 |
| Popular Vote1: | 42,745 |
| Percentage1: | 56.23% |
| Candidate2: | Trish DeBerry-Mejia |
| Colour2: | c0c0c0 |
| Popular Vote2: | 22,031 |
| Percentage2: | 28.98% |
| Candidate3: | Diane G. Cibrian |
| Colour3: | c0c0c0 |
| Popular Vote3: | 6,181 |
| Percentage3: | 8.13% |
| Mayor | |
| Before Election: | Phil Hardberger |
| After Election: | Julian Castro |
The San Antonio mayoral election of 2009 was held on May 9, 2009. The incumbent mayor Phil Hardberger was term-limited after serving two terms. The election was won by Julian Castro, who took office on June 1, 2009. The election was officially nonpartisan.
After the deadline to file passed, four candidates (Castro, Cibrian, McNeil and DeBerry-Mejia) were considered the frontrunners in the race. Polls showed Castro ahead by big margins, and some polls showed Castro winning outright without need for a runoff election. Second place was highly contentious, with Cibrian and DeBerry-Mejia trading off for second place.
On May 9, 2009, the election for Mayor was held. Turnout was slightly higher in the May 2009 election than the May 2007 election, with 11.61% of registered voters casting a ballot in the 2009 election (as opposed to 10.16% in 2007). Also, more votes were cast during early voting than on election day (55,780 votes cast during early voting to 34,055 on election day.)
A majority of votes is required to win the office of Mayor of San Antonio. If no person earns a majority, the two top vote earners shall advance to a runoff election to decide. Mayoral elections are non-partisan.
* Vote percentage only include votes for San Antonio Mayor. The remaining 1.78 percent in the election voted for different constituencies, or did not cast a vote for Mayor of San Antonio