The cellulose synthase genes were searched and analyzed by using the Cellulose_synt domain sequences identified from the CesA genes in plants as queries in NCBI and other genome databases. Phylogenetic trees of cellulose synthase gene from 171 sequences of CesA in 10 species including eudicot and monocot published on the GenBank were generated by MEGA4.0. The results showed that these cluster in groups wherein orthologs were often more similar than paralogs, indicating that different subclasses evolved prior to the divergence of the monocot and eudicot lineages. These CesA genes in eudicot and monocot were originated from seven genes. Based on the information of biosynthesis of primary or secondary wall by CesA gene regulation in model plant, the function of some unknown genes could be speculated from the trees.