The ubiquitin-proteasome system is composed by multiple enzymes which are ubiquitously expressed in mammalian cells and plays an essential role in a variety of biological processes. As key members of the protein degradation enzymatic system, the function of E3 ubiquitin ligases has been extensively investigated. BMP and TGF-β are critical molecules that regulate proliferation, differentiation and apoptosis of osteoblasts and chondrocytes through different signaling pathways. Resent findings indicate that the ubiquitin-proteasome system functions as a key regulator in bone cells and the E3 ligase mediates the proteolytic degradation of critical molecules in BMP and TGF-β signaling pathways. Recent progress on studies of HECT domain E3 ligase, Smurf, in osteoblasts and chondrocytes were summarized. The regulatory role of Smurf1 and Smurf2 in BMP and TGF-β signaling and osteoblast and chondrocyte function has been reviewed.