Four monoclonal antibodies (mAbs) to immunoglobulin M (IgM) of turbot Scophthalmus maximus were produced and characterized. All the mAbs (denominated B1D1, D5C2, E1B2 and F4A1) are showed good anti-turbot IgM reactivity in enzyme linked immunosorbent assay (ELISA) and immunoblotting. Results of ELISA indicated that the titre of the mAb was 1:1.024×10⁶ and the minimum detectable amount of IgM was 32 ng/mL. Results of immunoblotting showed that the mAb reacted with heavy chain of IgM. The mAb showed specificity for Scophthalmus maximus, light specificity for Paralichthys olivaceus, Takifugu rubripes, Sebastodes fuscescens, Hexagrammos otakii, Lateolabrax japonicas, and no specificity for Cynoglossus semilaevis, Cyprinus carpio, Carassius cuvieri, Ctenopharyngodon idellus, Aristichthys nobilis. The mAbs characterization should prove useful for studying the biology of IgM and its practical application.