Junenol based-eudesmanolides have been detected in many compositae plant species and were reported to exhibit various pharmacological activities. So far, the gene encoding junenol synthase has never been isolated. Here we report the molecular cloning and functional analysis of a 10-epi-junenol synthase from Inula hupehensis (designated IhsTPS1). IhsTPS1 converts the substrate farnesyl diphosphate into multiple sesquiterpenes with the product 10-epi-junenol being predominant. The transcript levels of IhsTPS1 correlate well with the accumulation pattern of 10-epi-junenol in I. hupehensis organs, supporting its biochemical roles in vivo.