Crews from Penarth lifeboat station were involved in an early morning rescue near Lavernock Point.
They were called out to a fishing boat which was taking on water. The boat quickly sank and RNLI crews took to the water to save the lives of the two casualties. They were transferred to Barry Dock lifeboat which had also been called in.
Both casualties were cold and taken to hospital for medical checks.
The operation also involved Wales ambulance service, rescue helicopter 187, Penarth Coastguard Rescue Team, and Milford haven coastguards.