The transcription factor Oct-4 is expressed specifically in mammalian preimplantation embryos and its function is related to the maintenance of embryonic stem cell pluripotency. The functional role of the heterogenous expression of Oct-4 remains unclear however. A GFP reporter construct, pOct-4(p)-GFP was generated, containing the upstream regulatory regions of bovine Oct-4 gene and its expression pattern was evaluated in the developing embryos of mouse, pig and rabbit following intracytoplasmic sperm injection. GFP fluorescence was visible early at the 2-cell stage and then became stronger in the blastocysts of all three species. However, the distribution of the GFP signals was restricted to the cells of inner cell mass and no fluorescence was detectable in trophectoderm cells. These results suggest that the bovine Oct-4 promoter is functional and that its embryonic expression activity is similar in different mammalian species.