The 11-foot long, 2 ton statue was taken from the courtyard of the Henry Moore Foundation in Perry Green, Much Hadham in Hertfordshire, Thursday night, the BBC reported.
Closed circuit TV showed three men loading the reclining figure into the back of a truck with a crane. They may have stolen it for its scrap value, police said.
"This is a very valuable statue and we are working closely with the Henry Moore Foundation to ensure its safe return," a police spokesman said.
The BBC said the foundation has offered a substantial reward for information leading to the recovery of the piece.