Abstract: Disclosed are (1) a Xenopus laevis bone morphogenetic protein (BMP), (2) a DNA comprising a DNA segment coding for a Xenopus laevis BMP, (3) a transformant bearing a DNA comprising a DNA segment coding for a Xenopus laevis BMP and (4) a method for preparing the Xenopus laevis BMP which comprises culturing the described in (3), producing and accumulating the protein in a culture, and collecting the protein thus obtained. Cells transinfected or transformed with the DNA allow large amounts of the Xenopus laevis BMP mature peptides to be produced, which causes the advantageous production of the peptides, which promote the synthesis of proteoglycan and can also be utilized for analysis of the mechanism of organism, particularly human bone-cartilage morphogenetic reaction, and as therapeutic agents for osteoporosis.