To produe high-purity cis-isoambrettolide by macrolactonizing cis-16- hydroxy-9-hexadecenoic acid or its ester.

A (non)esterified trans-16-hydroxy-9-hexadecenoic acid of formula I (wherein R1 is H or acetyl; and R2 is H or methyl) is trans-epoxidized; the resultant epoxide of formula II is ring-opened to give erythroalliulytic acid or its ester of formula II, which is reacted with an ortho ester of formula IV (wherein R" is methyl or ethyl); and the resultant dioxolane of formula V is thermally decomposed. Thus is obtd. cis-16-hydroxy-9-hexadecenoic acid or its ester of formula VI having a purity of 99 wt.% or higher, which is macrolactonized to give cis-isoambrettolide.