Rapid amplification of cDNA ends (RACE) method was used to clone the full length of mevalonate diphosphate decarboxylase (MDD) gene in Eleutherococcus senticosus.Then,the gene was analyzed by bioinformatic method and its expression patterns in different organs and different developmental periods were tested by RT-PCR.The results were as follows:(1)The full length of MDD cDNA sequence was 1 769 bp containing a 1 263 bp ORF that encoded 420 amino acids.The deduced amino acids sequence of MDD exhibited specific recognition sequence of GHMP kinase super family,and the accession number of MDD gene was JQ905594.In the secondary structure,the protein contains 161 alpha helixs,takes up 38.33%,68 extended strands,takes up 16.19%,19 beta turns,takes up 4.52%,172 random coils,takes up 40.95%.Without transmembrane domain,MDD was located in the outer membrane region.(2)RT-PCR results showed that MDD gene expressed in different developmental periods and different organs of E.senticosus,and the gene expression significantly differed among the periods or organs (P<0.05).The expression pattern of MDD,was likely to firstly raise in the period from bud germination to fully expanding of leaves,then decrease to the lowest content,and finally raise to another peak level when the fruits grow with a high speed.The highest expression (in fully expanding leaves) was 4.51 fold to the lowest expression (in aging leaves).The highest gene expression was detected in young shoots,which was 7.22 fold to the lowest level in leaves.However,no significant difference was detected among leaves,petioles and roots.The results had profound effect on the better understanding of the biosynthesis and regulation of E.senticosus saponins.