Novel sesquiterpene lactones, (6R)-pseudomajucin (1) and merrillianin (3), have been isolated from the pericarps of Illicium merrillianum, and their structures have been elucidated on the basis of the spectral data. A methanol solution of (6R)-pseudomajucin coexisted with (6R)-pseudomajucinone (2) in a keto/acetal equilibrium, whereas the crystals solely consisted of a keto-type 2, the structure of which was established by X-ray crystallographic analysis. The absolute stereochemistry of 1 was determined by the X-ray crystallographic analysis of its 7-O-methyl-3-O-p-bromophenylcarbamate. Merrillianin (3) is a unique seco-prezizaane-type sesquiterpene with an unprecedented dilactone moiety, which may be biosynthesized from pseudomajucin (4) or (6R)-pseudomajucin (1) by oxidative cleavage of the C-6/C-7 bond.