One new halimane diterpenoid, marrubasch C (1), two new labdane diterpenoids, marrubaschs D and E (2 and 3), and three known labdane diterpenoids, marrubasch F (4), marrubiin (5), and marrubenol (6), were isolated from the ethanol extract of Marrubium aschersonii Magnus (Lamiaceae). Structures of these compounds were elucidated on the basis of spectroscopic analysis. The inhibitory effects of compounds 1–6 on nitric oxide (NO) production in RAW 264.7 macrophage cells activated by lipopolysaccharide (LPS) were investigated and all the compounds showed weak activity.