Triterpenes are natural products of plants that can defend against microorganisms and various stresses. Oxidosqualene cyclase (OSC), the key rate-limiting enzyme of the triterpene biosynthetic pathway, catalyzes 2,3-oxidosqualene into sterols and triterpenes with different skeletons through the chair–boat–chair (CBC) conformation or chair–chair–chair (CCC) conformation. They were expanded in plants mainly by tandem duplication and are distributed in many plant lineages. They have multiple biological activities, including as functional foods and drugs. Here, we summarize the current characterized forest OSCs and their potential functions, especially for pharmacological applications. The study of triterpene-catalyzed enzyme OSC has an important scientific role and potential economic value. This paper summarizes the research advances of the main members of the OSC family in plants, their structure and function, the biosynthesis of triterpenes, and the molecular evolution of OSC.