Items of silverware and jewellery of "national importance" have been stolen from Court Barn Museum in Chipping Campden, Gloucestershire.
Among the items taken were objects created by designer and architect CR Ashbee, one of the pioneers of the Arts and Crafts movement.
Police said the burglary happened between 23:30 GMT and 23:40 GMT on Monday.
The museum said up to 30 objects, worth more than £30,000, were stolen.
Curator Sarah McCormick Healy said the objects which had been stolen were "very important items nationally and locally".
"They are unique items that were designed and made by individual craftsmen, which is what the museum celebrates," she said.
One of the objects taken was a silver brooch inlaid with jewels in the shape of a peacock, which was made by CR Ashbee.
The Arts and Crafts Movement began in the Cotswolds in the early 20th century, and CR Ashbee settled in Chipping Campden in 1902.
Talented artists, designers and craftspeople have worked in and around Chipping Campden and the north Cotswolds since the time of the Arts and Crafts movement. The Museum celebrates their lives and their skill.
Court Barn Museum,
Church Street, Chipping Campden, Gloucestershire GL55 6JE
Tel: 01386 841951
Source: BBC News Gloucestershire
Police said the intruders forced their way into the museum before smashing several glass display cabinets.
The stolen objects were all made between 1902 and about 1930.