Objective: To investigate whether CKLF-like MARVEL transmembrane domain-containing protein 2 (CMTM2) is involved in spermatogenesis in mice. CMTM2 is highly expressed in testis, and could possibly be a potential spermagogenesis specific gene.Methods: CMTM2-deficient mouse model was generated. Northern, RT-PCR and Western blotting analysis were performed on total RNA derived from wild-type (WT, CMTM2 ^+/+) and CMTM2 ^+/- (heterozygote) and CMTM2 ^-/-(homozygote) mice to examine the CMTM2 level. The number of litters and the number of pups were counted and pregnancy rates calculated. The motility and morphology of the sperm and the histology of testes were analyzed. Se-rum testosterone and FSH concentrations were also measured. Standard t-tests were used and standard error of means were calculated.Results: CMTM2 was highly expressed in a finely regulated pattern in the mouse testis during spermatogenesis. The body weight of adult mice with CMTM2 deficiency was not significantly different from that of wild type mice. No obvious anatomical or behavioral abnormalities were observed. The testis of CMTM2 ^-/- was smaller than that of CMTM2 ^+/+ mice. The testis diameter in wild mice and CMTM2 null mice were (11.32±1.21) mm vs. (8.29±1.92) mm (P<0.05), and the weights were (101.63±2.33) mg vs. (85.22±2.84) mg (P<0.05), respectively. Female CMTM2 null mice were fertile, indicating that CMTM2 was not required for female gametogenesis. The CMTM2 ^-/- mice produced virtually no sperm, and CMTM2 ^+/- mice sperm count showed a significant decline. In terms of sperm morphorlogy study, more round spermatids could be observed in the heterozygote group, compared with the wild type group; while in the homozygote group, a large amount of round spermatids could be observed because of complete arrest of spermiogenesis. The hormone levels were not significantly different. The CMTM2 ^-/- male mice were sterile due to a late, complete arrest of spermiogenesis. The organized architecture of the seminiferous epithelium of the seminiferous tubules seen in CMTM2 ^+/+ mice was lost in CMTM2 ^-/- mice. Conclusion: This study suggests CMTM2 is not required for embryonic development in the mouse but is essential for spermiogenesis, however, further studies are required for more detailed mechanism study.