Monoterpenes are important for plant survival and useful to humans. In addition to their function in plant defense， monoterpenes are also used as flavors， fragrances and medicines. Several metabolic engineering strategies have been explored to produce monoterpene in tobacco but only trace amounts of monoterpenes have been detected. We investigated the effects of Solanum lycopersicum 1-deoxy-d-xylulose-5-phosphate synthase (SlDXS)， Arabidopsis thaliana geranyl diphosphate synthase 1 (AtGPS) and Mentha × piperita geranyl diphosphate synthase small subunit (MpGPS.SSU) on production of monoterpene and geranylgeranyl diphosphate (GGPP) diversities， and plant morphology by transient expression in Nicotiana benthamiana and overexpression in transgenic Nicotiana tabacum. We showed that MpGPS.SSU could enhance the production of various monoterpenes such as (-)-limonene， (-)-linalool， (-)-α-pinene/β-pinene or myrcene， in transgenic tobacco by elevating geranyl diphosphate synthase (GPS) activity. In addition， overexpression of MpGPS.SSU in tobacco caused early flowering phenotype and increased shoot branching by elevating contents of GA and cytokinins due to upregulated transcript levels of several plastidic 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway genes， geranylgeranyl diphosphate synthases 3 (GGPPS3) and GGPPS4. Our method would allow the identification of new monoterpene synthase genes using transient expression in N. benthamiana and the improvement of monoterpene production in transgenic tobacco plants.