Epididymis plays a crucial role in regulating the development of sperm motility and fertilizing capacity. To study the function of genes in the caput epididymidis using the Cre/loxP system, we generated Lcn5-Cre transgenic mice in which the expression of Cre recombinase is driven by the 1.8-kb Lcn5 promoter. A total of 11 founder mice carrying the Lcn5-Cre transgene were identified by PCR from 38 offspring, and the integration efficiency was 28.9%. However, only 1 of the 11 transgenic mouse lines were revealed with the Cre recombinase expressed specifically in caput epididymidis. Furthermore, expression of Cre mRNA was first observed on Postnatal Day 30 and continued to increase during development. Subsequently, Cre protein distribution was assessed by crossing Lcn5-Cre transgenic mice into the mT/mG reporter line. As expected, the Cre recombinase activity was only found in principal cells of the middle/distal caput epididymidis. The tissue-specific expression of Cre protein in the caput epididymidis was further confirmed using Lcn5-Cre mice crossed with a mouse strain carrying Aip1 conditional alleles (Aip1^flox/ ). In summary, a transgenic mouse line expressing Cre recombinase in principal cells of caput epididymidis was established. This transgenic mouse line can be used to generate conditional, caput epididymidis-specific knockout mouse models by crossing with mice harboring floxed (LoxP flanked) genes.