Many invertebrates, including the mollusks, have been researched as potential source of compounds with antibiotic activity. Biochemical profile of the mucus from the slug Phyllocaulis boraceiensis was studied to determine if this species presents any fraction containing this sort of compound. Assays to quantify lipids, proteins, or peptides, free glucose or associated with other substances, were performed through establishment of the electrophoretic profile, high-performance liquid chromatography (HPLC), and mass spectrometry. The data were: lipids = 6.9 × 10-5 mg/mL; protein = 1.15 × 10-4 mg/mL; few amino acids were detected, probably because the molecules degraded; free glucose = not detected; glucose in association with other substance = 600 μg/mL. In the HPLC assay, some bands of protein were detected correlating with the electrophoretic profile. The mass spectrometry showed a major proteic component of 17.5 kDa molecular weight. Any direct bactericidal or bacteriostatic effect was detected facing distinct bacteria of medical interest such as Escherichia coli and Staphylococcus aureus. It could be hypothesized that eventual active compounds are masked in the mucosal matrix of the secretion. Probably the P. boraceiensis mucus acts as a physical barrier, hindering the entrance of microorganisms in the body, does not act on the microorganisms assayed-or even does not present microbicidal property.