Abstract: The chemical constituents of Rehmanniae Radix Preparata were prepared according to the traditional method of "jiu zheng jiu shai" and investigated using multiple chromatographic methods. Six alkaloids were isolated and their structures were elucidated from spectral data and physicochemical properties, as follows:rehmanniae alkaloid A (4-(5-O-á-D-galactopyranosyloxy)methyl-1H-pyrrole-2-carbaldehyde-1-ylbutyric acidmethyl ester) (1), baimantuoluoamide B (2), capparisine C (3), harman-3-carboxylic acid (4), (2S)-1-2-(furan-2-yl)-2-oxoethyl-5-oxopyrrolidine-2-carboxylate (5), and 1-2-(furan-2-yl)-2-oxoethylpyrrolidin-2-one (6). Among them, compound 1 is a new alkaloid. Compounds 2-6 were newly isolated from Rehmannia glutinosa Libosch. The effect of compounds 1-6 on NRK-52e cell injury induced by LPS was investigated. The results show that compounds 1-3 exhibit protective effects against LPS-induced damage to NRK-52e cells.