Grass Wood is an ancient woodland of 88 hectares (220 acres) in Wharfedale, North Yorkshire, England, that has an exceptional of woodland wildflowers. The area was notified as a Site of Special Scientific Interest in 1955 for upland broadleaved woodland. The site is also listed in A Nature Conservation Review under the entry for "Conistone Old Pasture and Bastow Wood". The Yorkshire Wildlife Trust completed the purchase of the site in 1983 and manages it as a nature reserve. The whole of the area of the SSSI is registered common land.