A novel chlorinated diterpene quinone methide; chlorosmaridione (7-chloro-11-hydroxy-abeita-7,9(11),13-triene-6,12-diode) was isolated from petroleum ether extract of the stems of Rosemarinus officinalis L. growing in Egypt. In addition, ${eta}-sitosterol$, stigmasterol, lupeol acetate, ${alpha}-amyrin,;{eta}-amyrin$, lupeol, acetyloleanolic acid, acetylursolic acid taxodione, horminone, and cryptotanshinone were also identified. Chemical structures of the isolated compounds have been elucidated on the bases of physical, chemical, and spectral data including IR, UV, MS, 1D-and 2D-NMR spectra.