An antibody capable of recognizing antigenic determinant(s) located on the FR-900506 substance, a highly-sensitive enzyme immunoassay method for the FR-900506 substance, which comprises immobilizing an antibody capable of recognizing antigenic determinant(s) located on the FR-900506 substance, allowing the FR-900506 substance contained in a sample and an enzyme-labeled FR-900506 substance to react competitively with the immobilized antibody and detect­ing the enzyme-labeled substance bound to the immobilized antibody, and a test kit for the detection of the FR-900506 substance. The invention also comprises a process for preparation of the monoclonal antibody of claim 4, which comprises culturing a hybridoma cell line capable of producing anti-FR-900506 substance antibody and isolating it from the cultured broth.