Objective To explore the expression of BAX during mouse kidney development. Methods Fifty-four mice from embryonic day 16, 18 and postnatal day 1, 3, 5, 7, 14, 21 were chosen to investigate the expression of BAX on epoxy sections of different development phases of mouse kidney with immunohistochemistry technique and stereological methods. Results The immunohistochemical positive staining of BAX was mainly observed in proximal tubules. During development, the expressive position of BAX gradually moved from deep to middle cortex, and finally was located on the superficial cortex. The numerical area density of BAX gradually increased from E16d to P3d, then descend, and turned to increase again at postnatal day 7. Conclusion During the development of kidney, the expression of BAX closely relates to the growth of proximal tubules, and may impact the proximal tubules in surviving, differentiating and maturing.