Purn Hill (grid reference ST332573) is a 6.1 hectare biological Site of Special Scientific Interest near the village of Bleadon, Somerset, notified in 1990.

The SSSI citation sheet describes the site as having an "exceptionally diverse unimproved calcareous grassland flora".

Over 200 species occur in the sward, including Salad Burnet (Sanguisorba minor), Dropwort (Filipendula vulgaris), Fairy Flax (Linum catharticum), Kidney Vetch (Anthyllis vulneraria) and Dwarf Thistle (Cirsium acaule).

Purn Hill is one of only five British sites for the nationally rare coastal limestone umbellifer species Honewort (Trinia glauca).

[1] Forty species of grass occur at the site, including Somerset Hair-grass (Koeleria vallesiana) which in Britain is confined to the western Mendips.