Abstract: The Citrus sinensis Ethylene -induced esterase genes (CsEIE) were studied to reveal their family爷s evolutionary history and their phylogentic realtionships. A total of 18 CsEIE gene family members were identified by analyzing the C. sinensis genome, and their homologs were also identified from several other plant species through searching TAIR, Phytozome and NCBI EST databases. The 18 members were comparatively analyzed for their gene structures, relative locations on chromosomes, protein domains and conserved regions, gene expression patterns, evolutionary direction and phylogenetic relationships. Results showed that the CsEIE genes were located on four different chromosomes, mostly as tandem repeats. The number of exons of the members varied from 1 to 5. Most of the members possessed 3 conserved motifs. Phylogenetic trees showed that EIE gene family members were clustered into three branches which were also prsenent in all analysed angiosperms, suggesting that EIE gene family is an ancient multigene family existing before the branching of angiosperms, and the current status of this gene family should be a result of gene duplication and gene differentiation. In the phylogenetic tree, CsEIE1 -CsEIE8 were clustered together independently, indicating they were derived from other species through gene duplication events after divergence from their common ancestor. Expression analysis showed that the transcriptional activity and expression patterns of CsEIE gene family were greately different. All the results indicte that the CsEIE gene family is still expanding and the members are experiencing different selection pressures