The constituents of five Costa Rican ferns of Preridaceae were investigated. The ferns and isolated compounds are as follows. Acrostichum aureum : quercetin 3-O-β-D-glucoside (I), ponasterone A (III). Neurocallis praestantissima : 2-deoxy-D-glucose (IV), 3, 6-anhydro-2-deoxy-D-glucose (V). Pteris podophylla : 6-(2-chloroethyl)-2 (S)-hydroxy-methyl-5, 7-dimethylindan-1-one (X), pterosin G (XI), kaempferol 3, 7-di-O-α-L-rhamnoside (II), apigenin 7-O-β-D-glucoside (VI), luteolin 7-O-β-D-glucoside (VII). Pteris livida : pterosin C (VIII), pterosin S (IX), 9-hydroxy-15-oxo-ent-kaur-16-en-19-oyl-β-D-glucoside (XII), 6β, 11β-dihydroxy-15-oxo-ent-kaur-16-en-19-oyl-β-D-glucoside (XIII), 6β, 9-dihydroxy-15-oxo-ent-kaur-16-en-19-oyl-β-D-glucoside (XIV), paniculoside III (XV), ptero-kaurene L₁ (XVI), 11β-hydroxy-15-oxo-ent-kaur-16-en-19-oic acid (XIX). Pteris altissima : VII, XI, XII, XIII, XV. Among the above products, X, XII, XIII and XIV are new compounds and their structures were elucidated by chemical and physicochemical methods.