Full-thickness incisional wounds were made on the dorsal skin of 1-day-old rats to elucidate the mechanism of the fluctuation of the epidermal thickness after the wound closure. The thickness of the epidermis covering the wound reached a peak around 96 h post-wounding (PW), and became thinner thereafter. The analyses of the cell proliferation and apoptosis at the epidermal wound regions revealed that the rate of TUNEL-positive cells that displays the cells undergoing apoptosis increased as the epidermis became thinner around 120 h PW. Next, immunohistochemical analyses using antibodies against keratinocyte differentiation marker proteins indicated that the delay or interruption of the spinous to granular transition from 96 to 120 h PW might result in the epidermal thickening in the wound region. Third, the region undyed with anti-caspase-14 antibody extended downward in the thickened epidermis by 96 h PW, and in turn, it became intensely and widely stained with this antibody in the thinning epidermis by 120 h PW. Taken together, it is likely that the delay and acceleration of the terminal differentiation, including cornification of the epidermal keratinocytes may coordinately cause the fluctuation of the thickness of the epidermis at the wound site in rat neonates.