Abstract: From Salvia trijuga Diels 9 compounds were isolated and eight of them identified as ferruginol, sugiol, triacontanoic acid, tetratriacontanoic acid, octacosanoic acid, hexactecanoic acid, dl-homoserine and parahydroxybenzoic acid. Compound Ⅰa red needle crystal C₂₀H₂₀O₅, mp 113～114℃ is a new diterpenoid related to methyltanshinonate named trijuganone C. Its structure has been proved to be 15, 16-dihydromethyltanshinoate by spectroscopic and chemical means.