Two new sulfated sesquiterpenoids, megastigman-7-ene-3, 5, 6, 9-tetrol-3-O-β-D-6'-sulfonated-glucopyranoside (1) and 3-O-β-D-6'-sulfonated-glucopyranosyl-6-(3-oxo-2-butenylidenyl)-1, 1, 5-trimethylcyclohexan-5-ol (2), along with one known sesquitepenoid compound icariside B1 (3) were isolated from the whole herb of Petasites tricholobus Franch. Their structures were identified by their chemical and spectroscopic characters. All obtained compounds were tested for their cytotoxicity against four cancer cell lines.