The jug was on display in a high security display cabinet when it was taken on Saturday between 11pm and 11.25pm.
‘The Wenlok Jug’ bronze jug is a rare example of metalwork that can be associated with royalty from the 1400s. It stands at 31.5cm in height, weighing 6.1kgs and it's decorated with coats of arms, inscribed with the words “My Lord Wenlok”.
Karen Perkins, Director of Museums, said: "This is an extremely serious and upsetting situation.
"The Wenlok Jug is a nationally significant medieval object, which came close to being lost to the UK when it went up for sale with Sotheby’s in May 2005.
"However, a temporary export ban provided the opportunity to raise funds to secure the purchase of the Jug. Due to the fundraising work undertaken in Luton and the generosity of funders and donors, the Jug was able to be purchased and to remain in the UK.
"We are extremely proud that the Wenlok Jug is part of the collections at Stockwood Discovery Centre and are working extremely closely with police and investigators to do all we can to recover it. Should anyone have any information about this theft, I would ask that they please contact Bedfordshire Police right away."
Bedfordshire Police have now launched an investigation.