Great Cressingham Fen is a 14.3-hectare (35-acre) biological Site of Special Scientific Interest near Great Cressingham in Norfolk. It is part of the Norfolk Valley Fens Special Area of Conservation.

This calcareous spring-fed valley has a variety of vegetation types, ranging from dry unimproved grassland on high slopes to tall fen where the springs emerge at the valley bottom. There is a diverse range of flora, including some uncommon species. Plants in the valley bottom include water mint and southern marsh orchid.

The site is private land with no public access.