The total cell number is the most fundamental data to correctly analyze the development of the tissues and organs. In the present study, we focused on the intestinal epithelium during the period of the intestinal elongation and villi formation. We first measured by using stereology the total number of the intestinal epithelial cells from junction between the stomach and duodenum to the cecum of C57BL/6J mouse embryos at embryonic day (E) 11.5, E13.5, and E15.5 during which the intestine elongates rapidly and the villi start to be formed. We then mathematically analyzed the total epithelial cell number data and formulate the proliferation. The results suggest that the intestinal epithelial cell proliferation is exponential and expressed using the same formula with that for rapidly growing in vitro cultured cells during the log phase. The mechanism which supports the exponential cell growth and the biological significance are discussed.