Mountain pepper (Litsea cubeba (Lour.) Persoon) is an evergreen tree in the Lauraceae family and has attracted attention for the antioxidant and antibacterial effects of its essential oils. The dominant components of the essential oil of L. cubeba are monoterpenes. To investigate the biosynthesis of monoterpenes that have bioactivity in L. cubeba, three cDNAs corresponding to monoterpene synthase genes were isolated, and the corresponding enzymes were functionally characterized in vitro. The genes obtained were named LcTPS1, LcTPS2, and LcTPS3. Transcript levels for LcTPS1 were most prominent in the leaf tissues, and levels of LcTPS2 and LcTPS3 were more evident in fruit tissues than in leaf tissues. Phylogenetic analyses indicated that LcTPS1, LcTPS2, and LcTPS3 all belong to TPS-b subfamily of angiosperm monoterpene synthases. For each genes, the corresponding enzymes were expressed and functionally characterized. LcTPS1 converted geranyl diphosphate to trans-ocimene, and LcTPS2 converted geranyl diphosphate to α-thujene, while LcTPS3 is a mutifunctional enzyme that converted geranyl diphosphate to α-thujene and (+)-sabinene, respectively.