The 78th parallel south is a circle of latitude that is 78 degrees south of the Earth's equatorial plane in the Antarctic. The parallel passes through the Southern Ocean and Antarctica.
Starting at the Prime Meridian and heading eastwards, the parallel 78° south passes through:
| Co-ordinates | Continent or ocean | Notes |
|---|---|---|
| Antarctica | Queen Maud Land, claimed by | |
| Western Australian Antarctic Territory, claimed by | ||
| Adélie Land, claimed by | ||
| Eastern Australian Antarctic Territory, claimed by | ||
| Ross Dependency, claimed by | ||
| Southern Ocean | Ross Sea, south of the Pacific Ocean | |
| Antarctica | Ross Dependency, claimed by | |
| Marie Byrd Land, Unclaimed territory | ||
| Antártica Chilena, claimed by | ||
| Territory claimed by and (overlapping claims) | ||
| Territory claimed by, and (overlapping claims) | ||
| Territory claimed by and (overlapping claims) | ||
| Southern Ocean | Weddell Sea, south of the Atlantic Ocean | |
| Antarctica | Territory claimed by and (overlapping claims) | |
| British Antarctic Territory, claimed by | ||
| Queen Maud Land, claimed by |