ABSTRACTAs the hybrid between cattle and yak, cattleyak is a typical male sterile mammal, and the underlying mechanism for its spermatogenic arrest is still unclear. In this study, the coding region of cattleyak TAF4B gene was cloned by RT‐PCR and analysed by bioinformatics. To investigate the effects of TAF4B on cellular proliferation and differentiation, an expression vector was generated and introduced into undifferentiated spermatogonia (UDSPG) of cattleyak. The results showed that the protein encoded by TAF4B did not contain the signal peptide sequence. The expression level of TAF4B in UDSPG of cattleyak was lower than that in yak, while the overexpression of TAF4B in cattleyak promoted the proliferation activity of cattleyak UDSPG. Meanwhile, the expression of proliferation and meiosis‐related genes was increased but the differentiation‐related genes were decreased. Therefore, the aberrant expression of TAF4B in cattleyak UDSPG possibly impaired its proliferation and differentiation equilibrium and decreased its growth potentiality, thereby reducing the quantity of UDSPG and affecting spermatogenesis. This study provided a potential approach for further elucidation of the mechanism of spermatogenesis arrest and provided a new idea for solving the problem of male infertility in cattleyak.