Abstract: The effects of solvent and species on the constituents of the extracts from the barks of beefwood (Casuarinas) were investigated, and activities of the extracts to scavengehydroxyl free radicals were determined with phenanthroline-Fe(Ⅱ) oxidation assay. The results showed that solvents influenced greatly constituents and molecular weight distribution of the extract. The mixture of water and acetone containing 1.0% HCl(HAW) increased significantly the contents of total dry substance and polyphenols in the extract. The molecular weight of the extract from barks of C.junghuhniana by HAW was between 5×102 and 2×105. The extracts exhibited excellent scavenging activity tohydroxyl free radicals, and the scavenging rate was 81.6% at 2 g/L concentration of HAW extract. The scavenging rate tohydroxyl free radicals was affected deeply by the constituents of the extract.