The four, nicknamed "The Dollies," are said to be exact genetic copies of their predecessor who was put down seven years ago due to health problems, The Daily Telegraph reported Tuesday.
"Dolly is alive and well. Genetically these are Dolly," Professor Keith Campbell, who keeps the Dollies as pets on land at Nottingham University, told the British newspaper.
The arrival of the original Dolly was a landmark in genetic technology, demonstrating that scientists could convert an adult sheep's cell into an embryo, which was then grown into a new sheep.
Her birth prompted a fierce debate about the ethics and ramifications of cloning, with the ethical arguments against animal cloning strengthened by the ill health that forced her to be euthanized.
Campbell said the latest experiments were carried out to determine if improvements to the technique could cut the risk of problems before and after birth.
The new Dollies are in good health, he said.
"They have got the life of Riley -- they potter around and get fed," he said.
"We are not doing anything to them, they have no health concerns and they show none of the signs of developing the arthritis that Dolly had."
Copyright 2010 United Press International, Inc. (UPI).