Abstract: An organic aluminum compound has been isolated from the roots of Prismatomeris tetrandra (Roxb) K Schum. This compound was shown to have protective effects on experimental silicosis in rats. The aluminum principle seems to be a complex compound according to its IR, NMR and MS spectra. In addition, seven crystalline substances were separated, five of them were identified as 2-methyl-anthraquinone, rubiadine, rubiadine-1-methyl ether, damnacanthal and β-sitosterol on the basis of chemical studies and spectrometric analysis. The other two components are respectively anthraquinone and terpenoid in character.