Burkholderia pseudomallei and Burkholderia mallei are two closely related gram-negative bacterial species classified by the CDC as category B biowarfare agents. To develop monoclonal antibodies (MAbs) that can recognize as many different strains and/or clinical isolates of these two pathogens as possible, we immunized mice with heat-killed bacterial whole cells and membrane preparations from multiple strains and/or clinical isolates of B. pseudomallei and B. mallei. More than 100 different hybridoma clones that produced MAbs strongly reacting to B. pseudomallei and/or B. mallei have been developed. These MAbs were categorized into eight different groups according to their reaction specificity against different species of Burkholderia bacteria as well as the different nature of target antigens (LPS, capsule polysaccharides, proteins, and glycoproteins) on the bacteria they recognized. Characterization of this large panel of MAbs has demonstrated an interesting pattern of various antigenic epitopes shared by the different species of Burkholderia bacteria. More importantly, this study has revealed a pathogenicity-linked antigen epitope(s) on capsule-like polysaccharides found only in the pathogenic species of Burkholderia bacteria and a Burkholderia-specific antigen epitope(s) that did not exist in other gram-negative bacterial species. Our MAbs should prove to be highly valuable in the development of detection, diagnosis, and therapeutic applications against B. mallei and B. pseudomallei infections.