A method for measuring a fibronectin fragment which is easy to handle and has excellent measuring accuracy, specificity and reproducibility is provided. An anti-fibronectin fragment monoclonal antibody which reacts with a human fibronectin fragment but does not react with human fibronectin, a measuring reagent containing the monoclonal antibody, a method for measuring a fibronectin fragment which uses the monoclonal antibody and a hybridoma which produces the monoclonal antibody are provided.