The present invention provides an anti-BMP9 (Bone morphogenetic protein-9) monoclonal antibody or an antibody fragment thereof binding to human BMP9, a hybridoma producing the antibody or the antibody fragment, a DNA encoding the antibody or the antibody fragment, a vector comprising the DNA, a transformant obtained by introduction of the vector, a method for preparing the antibody or the antibody fragment using the hybridoma or the transformant, and a therapeutic agent comprising the antibody or the antibody fragment as an active ingredient. Further, the present invention provides a pharmaceutical composition comprising the antibody or the antibody fragment as an active ingredient for the treatment of anemia such as renal anemia, cancer anemia or the like, and a method for treating anemia such as renal anemia, cancer anemia or the like using the same.