Abstract: Three diterpenes including a new compoud were isolated from the whole plant of Siegesbeckia glabrescens Mak. The new one was named as neodarutoside and its structure was elucidated as ent-3α,15,16-trihydroxy pimarane 3,15-his- (β-glucopyranoside) based on the spectral evidence and chemical transformation.The other two were darutigenol and darutoside. Darutoside possesses the activity of termination of early pregnancy in experimental rats at a dosage of 20～40 mg/kg.