Sigma Octantis (σ Oct / σ Octantis) is a magnitude 5.5 star in the constellation Octans, located at roughly RA 21h 09m, decl. −88° 57'

Its position near the southern celestial pole makes it the southern hemisphere's pole star and counterpart to Polaris, the current North Star. To an observer standing at the South Pole, Sigma Octantis would appear almost motionless and all the other stars in the Southern sky would appear to rotate around it.

Sigma Octantis is sometimes called Polaris Australis, or South Star. However, it is a faint star—at magnitude 5.5 it is barely visible to the naked eye—which makes it a rather poor pole star, especially by comparison to the much brighter and easily visible Polaris.