Adenovirus E4 promoter-binding protein 4 (E4BP4), a mammalian basic leucine zipper (bZIP) nuclear transcription factor, was identified to be involved in cell survival and proliferation. Previous research data showed that the expression of E4BP4 gene was up-regulated at the implantation sites on day 5 pregnancy of mouse. The aim of the present study was to examine the expression pattern of E4BP4 gene in uterus during pre-implantation period, and at the implantation sites and inter-implantation sites during the implantation process, through the Northern blot, in situ hybridization, Western blot and immunohistochemistry analyses. It was found that, (1) during the pre-implantation period, the expression of E4BP4 gene was gradually increased; (2) its expression was sharply up-regulated at the implantation sites compared with that at the inter-implantation sites during the embryo implantation process; (3) the uterine expression of E4BP4 gene was not embryo-dependent, but observed in artificially induced decidulization of pseudopregnant mouse; (4) both E4BP4 mRNA and E4BP4 protein were localized in stromal cells and decidual cells around the uterine lumen. These results indicated that E4BP4 may play a critical role in embryo implantation process by promoting stromal cell proliferation and inhibiting decidual cell apoptosis.