Abstract: Mu-feng-chin has been used as a diuretic and dropsic, etc. in Chinese medicine for many years. Four substances have been isolated by the author from a sample of Mu-fong-chi brought in Shanghai, and the details of the isolation and chemical properties of two of them, viz. Mu-fong-chin A and B, have been reported in previous papers of this series elsewhere. The present paper deals with Mu-fong-chin C, which has the molecular formula C₁₈H₂₁O₁₀ and a melting point 180-181℃. Mu-fong-chin C was shown to be a phenolic substance, it probably contains phenolic OH, methylenedioxy, aldehyde and methoxy groups.