Abstract: Mlo gene family is an important class of plant diseases resistance genes. Identification and sequence characterization of Mlo genes from the genome of castor (Riciuns communis L.) will lay the foundation for breeding for disease resistant varieties in castor. Based on systematic analysis of the genome sequence of Riciuns communis, a total of 16 Mlo genes were identified in this study, of which 15 contained a complete ORF and one partial sequence. Sequence analysis revealed that great difference were observed in the sizes of the 15 genes with complete ORF, however a conserved Mlo domain and 6 to 7 transmembrane domains were found in their corresponding protein sequences. These castor Mlo proteins were mainly located in plasma membrane. Phylogenetic analysis was performed to reveal the evolution of the castor Mlo genes with complete ORF, and Mlo genes from other species. The result indicated that the castor Mlo family could be devided into 7 clades (Ⅰ-Ⅶ). TheⅦclade contained only two castor Mlo genes (RcMlo8 and RcMlo9), which suggested that it might be a specific clade for castor genome. Furthermore, castor RcMlo3, RcMlo2, RcMlo6, and RcMlo12 were grouped into theⅣandⅤclades, which contain the Mlo genes of known function in disease resistance, suggested that the 4 castor Mlo genes might have their functions in disease resistance. These results will provide a good base for further cloning these castor Mlo genes and studying their biological functions.