Abstract: Because of their chemical properties, bacterial capsules tend to collapse during dehydration before electron microscopy. The purpose of this study is thus to evaluate the use of monoclonal antibodies (mAbs) against capsular material to stabilize and visualize bacterial capsule. Two important porcine pathogens with a known ultrastructure, namely, Actinobacillus pleuropneumoniae and Streptococcus suis, were used. Our data indicate that mAbs, either immunoglobulin G (IgG) or IgM, preferably from ascite fluids, can be used to stabilize bacterial capsular material in preparation for electron microscopy. However, because of their low antibody titer, the use of mAbs from culture supernatants is not recommended.