A new sesquilignan, erythro-Guaiacylglycerol-beta-O-4'-(5')-methoxylariciresinol, together with six known compounds including three sesquilignans and three dilignans, have been isolated from Campylotropis hirtella (Franch.) Schindl. that was used as traditional Chinese medicine for treatment of benign prostate hyperplasia. All these known compounds were found for the first time from the family leguminosae. The structure of the new compound and its relative configurations were elucidated on the basis of detailed spectroscopic analysis (NMR and MS). These compounds showed no obvious inhibition effect on prostate specific antigen secretion in LNCaP cells by ELISA method.