Recently, several bone morphogenetic protein (BMP) receptors (ⅠA, ⅠB and Ⅱ) have been cloned and characterized. BMP receptors belong to the TGFβ receptors family of serine/threonine kinases. Both typeⅠ and typeⅡ BMP receptors bind BMP ligands, in order to elicit a signal, heteromeric complexes of typeⅠ and typeⅡ receptors are required. Using truncated and constitutively active BMP receptors, it has been shown that type ⅠA BMP receptor plays important role in mesoderm formation in vivo. Type ⅠB BMP receptor plays major roles in chondrogenesis, osteoblast differentiation and programmed cell death in vivo and in vitro. BMP receptor signaling molecules Smad1 and Smad5 are also cloned and characterized. They also play important roles in BMP receptor mediated function.