Abstract: ObjectiveThe present study was conducted to clone and analyze the cation exchanger gene (CAX2) from two nicotiana genotypes in order to provide references for CAX2 function and mechanism in cadmium transportation of nicotiana . MethodBased on CAX2 sequence of potato in NCBI and EST sequences of Nicotiana the primers CAX2-F and CAX2-R were designed to clone CAX2 gene from K326 (Nicotiana tabacum) and Nicotiana. rustica by PCR technique. The sequence of CAX2 was analyzed by bioinformatics methods. ResultBoth of CAX2 coding region in K326 and N. rustica (named as NtCAX2 and NrCAX2) were 1314 bp in length, their nucleotide sequences shared with 98.0% of homology. Their deduced amino acids were 437 aa long with only existing 5 residues differences. Nt-CAX2 and NrCAX2 proteins shared with 98.9% of homology, had two identical Na+-Ca2+ exchange protein domains in 102-249 aa and 293-426 aa regions, and were characterized by common structure characteristics of CAX family. The theoretical pI of NtCAX2 and NrCAX2 were 5.54 and 5.45, respectively. Both of them had 11 transmembrane spans with obvious hydrophobicity and two repeat regions of α-1 and α-2, and richened in alpha helix. Phylogenetic analysis results found that , NtCAX2 and NrCAX2 had the closest relationship to potato (StCAX2) , and their protein homolo-gies were higher than 92 . 0%. ConclusionThe homology of CAX2 gene was very high in N. tabacum and N. rustica with different Cd accumulating pattern. The CAX2 gene was highly conserved in Solanaceae.