Penn's Rocks is a 10.2-hectare (25-acre) biological Site of Special Scientific Interest north of Crowborough in East Sussex.

[1][2] This site is a steep sided valley on sandstone with many mosses and liverworts, which is a nationally rare habitat.

Uncommon species include Orthodontium gracile, Bazzania trilobata, Saccogyna viticulosa and Harpanthus scutatus.

[3] This site is in four separate areas.

A footpath runs through one of them but the others are private land.