Lewes Downs is a 165-hectare (410-acre) biological Site of Special Scientific Interest east of Lewes in East Sussex. It is a Nature Conservation Review site, Grade I and a Special Area of Conservation. Part of it is a national nature reserve, part is Malling Down nature reserve, which is managed by the Sussex Wildlife Trust, and part is Mount Caburn, an Iron Age hill fort which is a Scheduled Monument.

This south-facing slope on the South Downs is ecologically rich chalk grassland and scrub. Flora include the nationally rare early-spider orchid and it also has a diverse invertebrate fauna and an important breeding community of downland birds.