Bone morphogenetic protein 4 (BMP4) regulates skeletogenesis, osteoblastic differentiation, and the induction of hair follicles. Its protein-coding region contains a signal peptide, prodomain (which regulates post-translational synthesis), and a mature domain (which mediates gene function). Previous studies considered this gene to be conserved. By reanalyzing the coding region of BMP4 in 16 mammalian species, we found that the mature domain is conserved in mammals. A comparison of the putative amino acid sequence demonstrates that BMP4 is relatively conserved. Two domains in BMP4 are connected by a random coil. The protein conformation differs between the Muridae family and other species, which might be associated with the body type of the former group.