Abstract: 【Objective】 To identify whole genome of Eucalyptus urophylla × Eucalyptus grandis CesA gene family and analyze its expression pattern， and to explore candidate genes with high expression in the stem， which could provide theoretical reference for exploring the function and regulatory mechanism of this family and improving fiber quality of Eucalyptus urophylla × Eucalyptus grandis.【Method】 Based on whole genome of Eucalyptus urophylla × Eucalyptus grandis， CesA gene family members of Eucalyptus urophylla × Eucalyptus grandis were identified， and gene structure， chromosome localization， and collinearity were analyzed， the physicochemical properties， subcellular localization， conserved domains， secondary structure， tertiary structure， and phylogenetic analysis were conducted. The relative expression of Eucalyptus urophylla × Eucalyptus grandis CesA gene family members in different buds， leaves， stems， and roots were detected using real-time fluorescence quantitative PCR.【Result】 A total of 15 CesA gene family members in Eucalyptus urophylla × Eucalyptus grandis were identified， and named EuCesA1-EuCesA15 according to their chromosome localization. The molecular weights of the 15 EuCesAs proteins ranged from 8027.03 to 123688.28 Da， and their theoretical isoelectric points ranged from 4.67 to 9.95. Most of them were unstable hydrophilic proteins. The 15 EuCesAs proteins were mostly located in the chloroplasts， and their secondary structures were mainly characterized by random coiling and α-helix. The 15 EuCesAs genes were unevenly distributed on 8 chromosomes， and 4 pairs of genes （EuCesA2 and EuCesA3， EuCesA4 and EuCesA9， EuCesA5 and EuCesA10， EuCesA8 and EuCesA13） had collinear relationship. Based on the phylogenetic analysis， the 15 EuCesAs proteins could be divided into group a and group b. The number and position of their conserved motifs were quite different， and the conserved domains they contained were also different. The results of real-time fluorescence quantitative PCR indicated that expression of most EuCesAs genes had tissue specificity. Among them， the relative expression of EuCesA2， EuCesA3， and EuCesA7 genes in the stem were significantly higher than those in the bud （P<0.05）， and EuCesA2 gene was highly expressed in both stem and root.【Conclusion】 The 15 selected members of CesA gene family in Eucalyptus urophylla × Eucalyptus grandis undergo a certain degree of differentiation， among them， EuCesA2 gene is expressed in the stem. It is speculated that it is involved in the synthesis of primary wall cellulose in young eucalyptus stems and the thickening of phloem fiber cell walls， thereby affecting cellulose content in wood and efficiency of biomass conversion.