The Union-Castle Line was a British shipping line that operated a fleet of passenger liners and cargo ships between Europe and Africa from 1900 to 1977. It was formed from the merger of the Union Line and Castle Shipping Line.

Union-Castle named most of their ships with the suffix "Castle" in their names; the names of several inherited from the Union Line were changed to this scheme (for example, Galician became Glenart Castle) but others (such as Galeka) retained their original name. They were well known for the lavender-hulled liners with red funnels topped in black, running on a rigid timetable between Southampton and Cape Town. Every Thursday at 4pm a Union-Castle Royal Mail Ship would leave Southampton bound for Cape Town. At the same time, a Union-Castle Royal Mail Ship would leave Cape Town bound for Southampton. In 1922 the line introduced its Round Africa service, a nine-week voyage calling at twenty ports en route. Alternate sailings travelled out via the Suez Canal and out via West Africa.

It merged with Bullard King and Clan Line in 1956 to form British & Commonwealth Shipping, and then with South African Marine Corporation (commonly referred to as Safmarine) in 1973 to create International Liner Services, but maintained its separate identity throughout. Its shipping operations ceased in 1977.