The stainability of mouse embryos with brilliant cresyl blue (BCB) and the development to blastocysts of BCB-positive and BCB-negative embryos were examined. From the 2-cell to the morula stages, the incidences of BCB-positive embryos collected from mature mice were 94.2 to 96.4%. These rates were significantly higher at all stages than those of BCB-negative embryos. The rates of development to blastocysts of BCB-positive embryos (85.7 to 96.7%) were significantly higher than those of BCB-negative embryos (0 to 50.0%) at all stages. In 2-cell embryos and morulae collected from aged mice, the incidences of BCB-positive embryos (79.5 and 58.6%) were significantly higher than those of BCB-negative embryos (20.5 and 41.4%, respectively). The rates of development to blastocysts of BCB-positive 2-cell embryos and morulae collected from aged mice were 77.1 and 79.4%, which were significantly higher than those of BCB-negative embryos, 0 and 45.8%, respectively. Although the incidences of BCB-positive embryos collected from aged mice were significantly lower than those collected from mature mice, the rates of development to blastocysts in BCB-positive embryos did not differ between the embryos collected from aged and mature mice. In these findings, we demonstrate that BCB-positive embryos have high developmental ability to the blastocyst stage. A correlation was also found between BCB stainability and G-6-PDH activity in mouse eggs and embryos.