| Fray Justo Santa María de Oro Department | |
| Native Name Lang: | es |
| Settlement Type: | Department |
| Mapsize: | 180px |
| Pushpin Map Caption: | Location of Fray Justo Santa María de Oro Department in Argentina |
| Coordinates: | -27.8167°N -70°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Argentina |
| Subdivision Type1: | Province |
| Subdivision Name1: | Chaco Province |
| Seat Type: | Head town |
| Unit Pref: | Metric |
| Area Total Km2: | 2,205 |
| Population Total: | 10,485 |
| Population Density Km2: | auto |
| Population Demonym: | Santasylvinense |
| Timezone1: | ART |
| Utc Offset1: | -3 |
| Postal Code: | H3541 |
| Area Code: | 03735 |
Fray Justo Santa María de Oro is the most south western department of Chaco Province in Argentina.
The provincial subdivision has a population of about 10,500 inhabitants in an area of 2,205 km², and its capital city is Santa Sylvina, which is located around 1,000 km from the Capital federal.
It takes its name from Justo de Santa María de Oro.