Geranylgeranyl diphosphate synthase (GGPPS, EC: 2.5.1.29) catalyzes the biosynthesis of geranylgeranyl diphosphate (GGPP), which is a key precursor for diterpenes including tanshinone. In this study, a full-length cDNA encoding GGPPS was isolated from Salvia miltiorrhiza by rapid amplification of cDNA ends (RACE) for the first time, which was designated as SmGGPPS (GenBank Accession No. FJ643617). The full-length cDNA of SmGGPPS was 1,234 bp containing a 1,092 bp open reading frame (ORF) encoding a polypeptide of 364 amino acids. Analysis of SmGGPPS genomic DNA revealed that it contained 2 exons and 1 intron. Bioinformatics analyses revealed that the deduced SmGGPPS had extensive homology with other plant GGPPSs contained all 5 conserved domains and functional aspartate-rich motifs of the prenyltransferases. Molecular modeling showed that SmGGPPS is a new GGPPS with a spatial structure similar to other plant GGPPSs. Phylogenetic tree analysis indicated that SmGGPPS belongs to the plant GGPPS super-family and has the closest relationship with GGPPS from Nicotiana attenuate. The functional identification in Escherichia coli showed that SmGGPPS could accelerate the biosynthesis of carotenoid, demonstrating that SmGGPPS encoded a functional protein. Expression pattern analysis implied that SmGGPPS expressed higher in leaves and roots, weaker in stems. The expression of SmGGPPS could be up-regulated by Salicylic acid (SA) in leaves and inhibited by methyl jasmonate (MeJA) in 3 tested tissues, suggesting that SmGGPPS was elicitor-responsive. This work will be helpful to understand more about the role of SmGGPPS involved in the tanshinones biosynthesis pathway and metabolic engineering to improve tanshiones production in S. miltiorrhiza.