Upper Teesdale is a Site of Special Scientific Interest (SSSI) in the west County Durham, England.

The Upper Teesdale SSSI is one of the most important botanical sites in Britain; [1] the flora is exceptionally rich in species that are nationally rare, including some that are relicts of the arctic-alpine environment of the last glacial period.

Following a substantial revision in 1990, most of the site was divided between two new (but adjoining) SSSIs, Upper Teesdale in Durham and Appleby Fells in Cumbria.

A small part was amalgamated with Moor House National Nature Reserve to form a third SSSI, Moorhouse and Cross Fell, which is contiguous with the other two.

At the same time, two further SSSIs, Mill Beck Wood and Moking Hurth Cave, were incorporated into Upper Teesdale SSSI and ceased to exist as separate entities.