Lye Valley is a 2.3-hectare (5.7-acre) biological Site of Special Scientific Interest in Headington, a suburb of Oxford in Oxfordshire.

[1][2] It is part of the 4.5-hectare (11-acre) Lye Valley Local Nature Reserve, which is owned and managed by Oxford City Council.

[3][4] The site contains a range of habitats including spring-fed lowland fen, dominated by rushes and sedges, a variety of ponds, and wet woodland with small representations of lowland calcareous grassland, wood pasture and parkland.

The plant and animal species of the Lye Valley fen are thought to have lived there since they colonised the spring areas after the retreat of the last ice age between eight and ten thousand years ago.

Rare plants include grass-of-Parnassus and marsh helleborine orchid, which are on the Red List of Threatened Species compiled by the International Union for the Conservation of Nature (IUCN).