Portsdown Hill is a long chalk ridge in Hampshire, England. The highest point of the hill lies within Fort Southwick at 131m above sea level. The ridge offers good views to the south over Portsmouth, the Solent, Hayling Island and Gosport, with the Isle of Wight beyond. The hill is on the mainland, just to the north of Ports Creek, which separates the mainland from Portsea Island, on which lies the main part of the city of Portsmouth, one of the United Kingdom's main naval bases. To the north lies the Forest of Bere, with the South Downs visible in the distance. Butser Hill can be seen on a clear day. The hill is formed from an inlier of chalk which has been brought to the surface by an east–west upfold of the local strata known as the Portsdown Anticline.
Catherington Down is a 12.8-hectare (32-acre) biological Site of Special Scientific Interest in Catherington in Hampshire. It is also a Local Nature Reserve
Beacon Hill, Warnford is a 46.4-hectare (115-acre) biological Site of Special Scientific Interest west of Warnford in Hampshire. It is a Nature Conservation Review site, and an area of 40.1 hectares is a national nature reserve. There is a round barrow cemetery dating to the Late Neolithic or Bronze Age on the hill, and this is a scheduled monument.
Seale Chalk Pit is a 1.2-hectare (3.0-acre) geological Site of Special Scientific Interest west of Guildford in Surrey. It is a Geological Conservation Review site and part of the Seale Chalk Pit and Meadow 3-hectare (7.4-acre) private nature reserve, which is managed by the Surrey Wildlife Trust.
Levin Down is a 25.6-hectare (63-acre) biological Site of Special Scientific Interest south of Midhurst in West Sussex. It is managed by the Sussex Wildlife Trust.
East Dean Park Wood is a 17.8-hectare (44-acre) biological Site of Special Scientific Interest south of East Dean in West Sussex.
Halnaker Chalk Pit is a 6.4-hectare (16-acre) biological Site of Special Scientific Interest north-east of Boxgrove in West Sussex.
Chinnor Chalk Pit is a 20.4-hectare (50-acre) geological Site of Special Scientific Interest south of Chinnor in Oxfordshire. It is a Geological Conservation Review site.
Avon Valley (Bickton to Christchurch) is a 1,403.8-hectare (3,469-acre) biological Site of Special Scientific Interest which stretches from Christchurch in Dorset to Bickton, south of Fordingbridge Hampshire. It is a Nature Conservation Review site, a Ramsar site, a Special Area of Conservation and a Special Protection Area. An area of 159 hectares (390 acres) is Blashford Lakes, a nature reserve managed by the Hampshire and Isle of Wight Wildlife Trust,
Broughton Down is a 45.8-hectare (113-acre) biological Site of Special Scientific Interest west of Broughton in Hampshire. The eastern half is a nature reserve managed by the Hampshire and Isle of Wight Wildlife Trust.
Coulters Dean is a 2.2-hectare (5.4-acre) biological Site of Special Scientific Interest south-east of Buriton in Hampshire. It is part of the 4-hectare (9.9-acre) Coulters Dean nature reserve, which is managed by the Hampshire and Isle of Wight Wildlife Trust.
Danebury Hill is a 13.7-hectare (34-acre) biological Site of Special Scientific Interest north-east of Nether Wallop in Hampshire. It is part of Danebury Hillfort Local Nature Reserve.
East Aston Common is an 18.2-hectare (45-acre) biological Site of Special Scientific Interest east of Andover in Hampshire.
Martin and Tidpit Downs is a 367.5-hectare (908-acre) biological Site of Special Scientific Interest north-west of Fordingbridge in Hampshire. Martin Down is a 341-hectare (840-acre) national nature reserve and an area of 115 hectares is a Nature Conservation Review site, Grade I. Bokerley Dyke, a prehistoric linear earthwork and scheduled monument, runs through the site.
Porton Down SSSI is a 1,559-hectare (3,850-acre) biological Site of Special Scientific Interest which spans the border between Hampshire and Wiltshire in England. It is adjacent to Porton Down science park near Porton, and much of it is Ministry of Defence property which is closed to the public. It is a Nature Conservation Review site, Grade I, a Special Area of Conservation and a Special Protection Area.
Quarley Hill Fort is a 3.5-hectare (8.6-acre) biological Site of Special Scientific Interest west of Grateley in Hampshire.
Rushmore and Conholt Downs is a 111.5-hectare (276-acre) biological Site of Special Scientific Interest north of Andover in Hampshire. It is a Nature Conservation Review site, Grade I.
Sidley Wood is a 11.7-hectare (29-acre) biological Site of Special Scientific Interest north of Andover in Hampshire.
Stockbridge Down is a 69.8-hectare (172-acre) biological Site of Special Scientific Interest east of Stockbridge in Hampshire. It is a Nature Conservation Review site, Grade 2. It is owned by the National Trust and part of it is a Scheduled Monument, with an Iron Age hillfort and fourteen Bronze Age burial mounds.
Toyd Down and Quarry is a 6.7-hectare (17-acre) biological Site of Special Scientific Interest east of Martin in Hampshire.
