Spermine synthase (SPMS, EC 2.5.1.22), enzyme of spermine (Spm) biosynthesis, has been shown to be related to stress response. In this study, attempts were made to clone and characterize a gene encoding SPMS from tea plant (Camellia sinensis). The effect of exogenous application of Spm in C. sinensis subjected to low-temperature stress was also investigated. A full-length SPMS complementary DNA (cDNA) (CsSPMS) with an open reading frame of 1113 bp was cloned using reverse transcription-PCR and rapid amplification of cDNA ends (RACE) techniques from cultivar "Yingshuang". The CsSPMS gene, which encoded a 371 amino acid polypeptide, in four cultivars is highly homologous. Quantitative real-time PCR indicated that the CsSPMS gene shows tissue-specific expression, mainly in the leaf and root of tea plant. The expression analysis demonstrated that the CsSPMS gene is quickly induced by cold stress and had similar trends in four cultivars. Spm-supplemented "Baicha" cultivar contains higher endogenous polyamines compared to the control, coupling with higher expression levels of ADC and SPMS. In addition, activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), as well as free proline content in the Spm-supplemented samples were higher than the control during the experiment course or at a given time point, indicating that Spm exerted a positive effect on antioxidant systems. Moreover, Agrobacterium-mediated expression of CsSPMS in tobacco leaves showed relatively higher cold tolerance. Taken together, these findings will enhance the understanding of the relationships among CsSPMS gene regulatory, polyamines accumulation, and cold tolerance in tea plant.