Gensac-sur-Garonne (French pronunciation: [ʒɑ̃sak syʁ ɡaʁɔn], literally Gensac on Garonne; Occitan: Gençac de Garona) is a commune in the Haute-Garonne department in southwestern France.

The commune is bordered by five other communes: Saint-Julien-sur-Garonne across the river Garonne to the north, Rieux-Volvestre to the northeast, Goutevernisse to the east, Saint-Christaud to the south, and finally by Cazères across the river Garonne to the west.

The river Garonne flows through the commune, making the suffix -sur-Garonne, forming a border between Saint-Julien-sur-Garonne and Cazères.

Historical population

Year	Pop.	±%
1962	229	—
1968	238	+3.9%
1975	189	−20.6%
1982	205	+8.5%
1990	249	+21.5%
1999	264	+6.0%
2008	323	+22.3%

• Communes of the Haute-Garonne department