Ethylene is a gaseous phytohormon in plants. Ethylene biosynthetic process involves three metabolic pathways: (I) the activated methyl cycle, (2) the S-methylmethionine cycle and (3) the methionine cycle (Yang cycle). The key enzymes in the ethylene biosynthesis are S-adenosylmethionine synthetase (SAMS), l-aminocyclopropane-I-carboxylic acid synthase (ACS) and l-amino-cyclopropane-I-carboxylic acid oxidase (ACO). Among them, SAMS catalyzes the synthesis of SAM ftom methionine and ATP. In this work, the authors have identified a total of four genes encoding SAMS enzyme in the genome of clementine tree. The SAMS are continuously encoding genes. In silico analysis results showed that the full-length predicted protein seuquences contain about 387-392 amino acids. All of SAMS proteins are acidic with pI values ranging from 5.52 to 5.82. The SAMS proteins of Clementine are highly homologous and they are similar to the SAMS of some other plants. The sequence analysis showed that the clementine SAMS proteins contains three conserved motifs which play a role as the enzymeatic active sites: GAGDQG, GGGAFSGKD and GHPDK. In addition, CclSAMS proteins also contain conserved amino acids which are the metal binding sites. The phosphorylation sites are identified in the CclSAMS proteins suggesting that these genes have post-transcription regulation mechanism. Secondary structure of all of four CclSAMS proteins includes 10 alpha helices and 12 beta sheets. Phylogenetic tree analysis showed that the CclSAMS are classified into two groups. Group I consists of 3 genes CclSAMSJ, CclSAMS2 and CclSAMS4, while the group II has only one, CclSAMS3. All of four CclSAMSs expressed in vegetative as well as reproductive tissues, or mixtures of them. The group I genes express more strongly as well as more differentially than the group II gene.