Pteris semipinnata is a fern species in the Pteridoideae subfamily of the Pteridaceae. It is native to Hong Kong. Trees or shrubs, 35-38cm tall. Six new ent-15-oxokauran-19-oic acid derivatives, named pterisolic acids A-F (1-6), were isolated from the ethanol extract of the fern Pteris semipinnata (Pteridaceae), and the structures of these new ent-kauranoids were elucidated on the basis of extensive spectroscopic studies and single crystal X-ray diffraction analysis. A new diterpenoid glucoside from Pteris semipinnata, The chemical investigation of the aerial parts of Pteris semipinnata afforded a new ent-kaurane diterpenoid glucoside, pteriside (1), and three known sesquiterpenoids, namely (2R)-pterosin B (2), (2S, 3S)-pterosin C (3) and pterosin C 3-O-β-D-glucoside (4). The structure of 1 was established by spectral methods, especially two dimensional NMR techniques.