Three 11-year-old tortoises – Squirtle, Wartortle and Blastoise – were stolen along with a 24-year-old male tortoise called Jeffery.
They were taken on the night of Wednesday 22 August after thieves are believed to have gained entry into a shed at the rear entrance of Kingston Maurward College, near Dorchester.
They made off with the tortoises by transporting them in a wheelbarrow.
The animals are between 40 and 50 cm long and 30 cm wide.
Police Constable Chris Stephens, of Dorchester police, said: “I am appealing to anyone who witnessed anything suspicious overnight in the area to please come forward.
“If you have any information that could assist with the investigation or have seen tortoises for sale in suspicious circumstances, please contact Dorset Police urgently.
“We are desperate to reunite them with the college to ensure they are appropriately cared for.”
:: Anyone with information is asked to contact Dorset police by calling 101.