The use of polysaccharides has gained prominence in the development of dressings such as films, sponges and gels that, in addition to providing the usual wound protection, can be antimicrobial vehicles or even intrinsically hold antimicrobial activity. In this context, the development of new antimicrobials from natural polymers has been shown to be relevant; and, chemical modifications of polymers in order to make them cationic can be a great alternative, given that polycationic charges can interact electrostatically with the negatively charged bacterial cell surface, causing antibacterial effects on them. In this sense, the aim of this study was to chemically modify the galactomannan gum extracted from the seeds of Dimorphandra gardneriana (GFD) in order to make it cationic and holder of antimicrobial activity. The gum was extracted and isolated and four modification routes were performed by quaternization (using N-3-chloro-2-hydroxypropyl trimethyl ammonium chloride - CHPTAC), varying the proportion of reagents, generating four quaternized derivatives (GQ1, GQ2, GQ3 and GQ4). The FTIR characterizations allow us to affirm that there was a modification of the GQ3 and GQ4 derivatives, with the appearance of bands in 1419 cm-1 that can be attributed to the introduction of quaternary ammonium groups in the GFD structure. The Zeta Potential analysis demonstrates a positive increase in charge of all modified gums compared to unmodified gum, such increases in charges indicate the presence of cationic groups in the modified gums Antimicrobial tests of minimal inhibitory concentration performed with all derivatives against Staphylococcus aureus and Staphylococcus epidermidis, showed that only GQ3 and GQ4 had an antibacterial effect against the tested bacteria, in which GQ4 showed better results, with a minimum inhibitory concentration of 31.25 μg/mL (S. aureus) and 15.62 25 μg/mL ( S. epidermidis). Elemental analysis revealed DS of 0.35 for GQ3 and 0.51 for GQ4, corroborating the efficiency of the modification with the FTIR data. Morphological analysis of the antibacterial effect of GQ4 on S. aureus and S. epidermidis through atomic force microscopy showed drastic changes in cell morphology, a significant increase in average roughness, resulting from the external alteration of cell surfaces, suggesting a possible cell rupture with extravasation of the cytoplasmic content. Cell viability tests using RAW 264.7 macrophages indicated that the mean cytotoxic concentration for all derivatives tested is greater than 35 mg/ml. Thus, GQ3 and GQ4 proves to be a promising anti-staphylococcal agent that can be optimized in the development of several antimicrobial formulations.