| Official Name: | Saint-Louis-du-Sud |
| Native Name: | Sen Lwi disid |
| Settlement Type: | Commune |
| Pushpin Map: | Haiti |
| Pushpin Label Position: | top |
| Pushpin Map Caption: | Location in Haiti |
| Subdivision Type: | Country |
| Subdivision Name: | Haiti |
| Subdivision Type1: | Department |
| Subdivision Name1: | Sud |
| Subdivision Type2: | Arrondissement |
| Subdivision Name2: | Aquin |
| Population As Of: | 2009 |
| Population Footnotes: | [1] |
| Population Total: | 59,042 |
| Coordinates: | 18.2667°N -73.55°W |
| Elevation M: | 9 |
Saint Louis du Sud (pronounced as /fr/; Haitian; Haitian Creole: Sen Lwi disid) is a coastal commune in the Aquin Arrondissement, in the Sud department of Haiti. Home to Fort des Oliviers, Fort Anglais and Bonnet Carré, the town is also the location of the 1748 Battle of Saint-Louis-du-Sud. Saint Louis du Sud is home to over 59,042 inhabitants.
On August 14, 2021 an M7.2 earthquake struck 12 kilometres (7.5 mi) northeast of the commune. It is the largest earthquake in Haiti since the M7.0 in 2010 that killed 316,000 people