Mill Green Museum is a working watermill in Hatfield, Hertfordshire, England.

The Domesday Book records several mills at Hatfield, and they are assumed to have included one at this site and another upstream at Lemsford.

However, the mill has been restored to full working order with 18th and 19th century wooden machinery.

It is in regular use to grind organic wheat for a local bakery and for retail sale on the premises.

Mill Green runs craft and baking workshops, children's activities and a school visit service.