Background: Preterm infants are susceptible to unique pathology due to their immaturity. Mouse models are commonly used to study immature intestinal disease, including necrotizing enterocolitis (NEC). Current NEC models are performed at a variety of ages, but data directly comparing intestinal developmental stage equivalency between mice and humans are lacking. Methods: Small intestines were harvested from C57BL/6 mice at 3–4 days intervals from birth to P28 (n = 8 at each age). Preterm human small intestine samples representing 17–23 weeks of completed gestation were obtained from the University of Pittsburgh Health Sciences Tissue Bank, and at term gestation during reanastamoses after resection for NEC (n = 4–7 at each age). Quantification of intestinal epithelial cell types and messenger RNA for marker genes were evaluated on both species. Results: Overall, murine and human developmental trends over time are markedly similar. Murine intestine prior to P10 is most similar to human fetal intestine prior to viability. Murine intestine at P14 is most similar to human intestine at 22–23 weeks completed gestation, and P28 murine intestine is most similar to human term intestine. Conclusion: Use of C57BL/6J mice to model the human immature intestine is reasonable, but the age of mouse chosen is a critical factor in model development.