【Objective】Xylan is the major component of secondary wall hemicellulose in dicot plants and plays an indispensable role in maintaining plant secondary wall integrity and plant growth. Xylan also greatly impacts wood properties and biomass energy. The study described here explores theIRX9 gene of Neolamarckia cadamba, a fast-growing tree species in southern China. Furthermore, the role of NcIRX9 in xylan biosynthesis is also explored. 【Method】 Bioinformatics was used to analyze NcIRX9 protein structure. A yellow fluorescent protein (YFP) fusion protein was constructed NcIRX9, and its subcellular localization was observed. Both NcIRX9 expression in different tissues were analyzed by qRT-PCR. In addition, by tissue sectioning and microscopic observation, chemical immunization, monosaccharide analysis, and H¹-NMR analysis, we verified the function of NcIRX9. NcIRX9 function was further validated in a mutant Arabidopsis model. 【Result】 NcIRX9 is evolutionarily conserved and contains a signal peptide at its N-terminus, closely related toArabidopsis AtIRX9, which is located in the Golgi. The NcIRX9 gene is expressed in the roots, stems, leaves, xylem and phloem, with its highest level of expression in the xylem. We determined that NcIRX9 can partially rescue the Arabidopsis mutant irx9 phenotype, as it is orthologous to AtIRX9. Moreover, this study also demonstrated that overexpression of NcIRX9 in Arabidopsis irx9 mutants increases xylose content, side chain signal enhancement, and reduces the end side chain signal enhancement. 【Conclusion】 The biological function of the NcIRX9 gene in Neolamarckia cadamba is similar to that of Arabidopsis AtIRX9 and is highly involved in xylan biosynthesis.