A protein having amino acid sequence in SEQ ID NO: 1 of the Sequence Listing derived from human MP52, and a dimer protein thereof. A homodimer protein described above can be obtained by constructing a plasmid containing DNA coding amino acid sequence in SEQ ID NO: 1 of the Sequence Listing with a methionine at the N-terminus, introducing the plasmid into E. coli for transformation, solubilizing inclusion bodies obtained by culturing the transformant, purifying the monomer protein from the solubilized solution, refolding the monomer protein into a dimer protein and purifying the same. The homodimer protein described above is useful as a pharmaceutical composition for treating cartilage and bone diseases.