tetraprenyl‐β‐curcumene synthase homologue from the alkalophilic Bacillus clausii catalyses conversions of a geranylfarnesyl diphosphate and a hexaprenyl diphosphate into novel head‐to‐tail acyclic sesterterpene and triterpene. Tetraprenyl‐β‐curcumene synthase homologues represent a new family of terpene synthases that form not only sesquarterpene but also sesterterpene and triterpene.