Mutalysin-II, from Lachesis muta muta snake venom, is an endopeptidase with hemorrhagic activity. To identify a conformational epitope we used Blue Star Sting, the latest version of the web based Sting Millenium Suite, as alternative computational analysis tool to select and design peptides. Pre-selected cut-off values of the accessibility and hydrophilicity parameters were used to select amino acid residues as potential conformational epitopes. A peptide (P117-Y116-C115-Q194-C195-L197-N198-K199-P200-Y5-L48) was manually drawn on Swiss-PDB-Viewer package and synthesized by Fmoc-synthesis. Immunization of rabbits with this peptide induced antibodies that recognized Mutalysin-II and protected against the hemorrhagic factors present in Lachesis venom. The Sting Millennium Suite was able to predict conformational epitopes in this class of proteins. Three amino acids (K199, Y5 and L48) were identified as essential in the interaction between the peptide and the neutralizing antibodies.