The southern fulmar (Fulmarus glacialoides) is a seabird of the Southern Hemisphere. Along with the northern fulmar, F. glacialis, it belongs to the fulmar genus Fulmarus in the family Procellariidae, the true petrels. It is also known as the Antarctic fulmar or silver-grey fulmar.

It is largely pale grey above and white below with a distinctive white patch on the wing. It breeds on the coast of Antarctica and on surrounding islands, moving north in winter. It nests in colonies on cliffs, laying a single egg on a ledge or crevice. Its diet includes krill, fish and squid picked from the water's surface.

The southern fulmar formally described and illustrated in 1840 by the Scottish zoologist Andrew Smith in his major work Illustrations of the Zoology of South Africa. He placed it with all the other petrels in the genus Procellaria and coined the binomial name Procellaria glacialoides. The southern fulmar is now placed with the northern fulmar in the genus Fulmarus that was introduced in 1826 by the English naturalist James Stephens. The genus name comes from the Old Norse Fúlmár meaning "foul-mew" or "foul-gull" because of the birds' habit of ejecting a foul-smelling oil. The specific epithet glacialoides combines the specific glacialis introduced by Carl Linnaeus in 1761 for the northern fulmar with the Ancient Greek -oidēs meaning "resembling". The species is monotypic: no subspecies are recognised. Molecular data suggests that the two fulmar species diverged during the Pleistocene epoch.

It is a fairly large, bulky petrel, 45 to 50 cm (18–20 in) long with a wingspan of 110 to 120 cm (43–47 in). The male has an average weight of 795 g (28.0 oz) while the smaller female weighs around 740 g (26 oz). These weights increase to 1,005 and 932 g (35.5 and 32.9 oz) at the start of a shift incubating the eggs. The male has a wing length of 34 cm (13 in), bill length of 44.6 mm (1.76 in), tarsus length of 52.1 mm (2.05 in) and tail length of 12.4 cm (4.88 in). The female has a wing length of 33.9 cm (13.3 in), bill length of 43 mm (1.69 in), tarsus length of 51.5 mm (2.03 in) and tail length of 12.1 cm (4.8 in).

The bird flies with a mixture of shallow flaps and long glides, often looking down to scan the water. The wings are fairly broad and rounded and are held stiff. The plumage is mainly pale silvery-grey above and white below. The head is white with a pale grey crown. The wingtips are blackish with a large white patch and the wings have a dark rear edge. The legs and feet are pale blue. The bill is pink with a black tip and dark bluish naricorns. First-year birds have a more slender bill than the adults.

It is usually silent but has loud, cackling calls which are uttered at the nest or in feeding flocks. Courting birds produce soft droning and guttural croaking calls.

There are colonies on a number of the islands around Antarctica such as the South Sandwich Islands, South Orkney Islands, South Shetland Islands, Bouvet Island, and Peter I Island. The bird also breeds at several sites along the mainland coast of Antarctica.

At sea, it mainly occurs along the outer edge of the pack ice in summer with water temperatures of −1.5 to 0.5 °C (29.3 to 32.9 °F). In winter, it regularly ranges north to around 40°S latitude. It occurs further north in the cool waters of the Humboldt Current, reaching Peru. Small numbers are seen off the coasts of South Africa, southern Australia and New Zealand. Many birds can be washed up on beaches after storms. There are several unconfirmed reports from the west coast of North America.