Twelve guaiane-type sesquiterpenoids, including four new ones, 10-O-methyl-orientalol A (1), 10-O-ethyl-alismoxide (2), 3β,4β-expoxy-chrysothol (3), orientalol G (4), and a new norsesquiterpenoid, orientalol H (5), were isolated from Chinese Alismatis Rhizoma, the dried rhizome of Alisma orientale.