〔Abstract〕 To construct a humanized mouse model of the interleukin-9 receptor (IL-9R) coding DNA sequence (CDS) gene and to verify the genotype and IL-9R expression in mice . Methods The CRISPR/Cas9 ge- nome editing technology was used to replace the exon2 - 7 fragment of the il-9r gene in mouse embryonic stem cells with the corresponding human IL-9R sequence . After verifying the completion of the gene fragment replacement , tetraploid embryos were constructed and microinjected back into the oviducts of surrogate mice . Through surrogacy by female mice , homozygous humanized mice were obtained . DNA was extracted from the homozygous humanized mice IL-9R CDS gene , and their genotypes were identified by agarose gel electrophoresis after PCR amplification . Western blot was used to detect the expression of IL-9R in the spleen and thymus of homozygous humanized mice with either wild-type ( WT) or IL-9R gene humanization . Results Gel electrophoresis after PCR amplification showed that mice with only a 1 805 bp band amplified using WT primers were wild-type , while mice with 2 553 bp and 2 340 bp bands amplified using 5KI and 3KI primers , respectively , were homozygous humanized mice with IL- 9R CDS gene . Western blot results indicated that the tissues of homozygous humanized mice model with IL-9R CDS gene expressed IL-9R significantly . Conclusion The humanized mouse model with IL-9R CDS gene has been suc- cessfully constructed and characterized .