Belsize Wood is a 0.7 hectare Local Nature Reserve and a Site of Borough Importance for Nature Conservation, Grade II, in Belsize Park in the London Borough of Camden. It is a steeply sloping site divided into a northern half, which is always open to the public and is of lesser ecological value, and a southern part which is in a better state of conservation, and which is only open at weekends. The two halfs are separated by a public footpath between Lawn Road and Aspern Grove. The site is owned and managed by Camden Council.
The site is deeply shaded and has a rich variety of species, especially of insects. The understorey is dominated hawthorn and elder, and the most common canopy trees are ash, sycamore and Swedish whitebeam. Ground level plants include butcher's-broom, enchanter's-nightshade and nettles. A number of common birds nest there.