Introduction: The growing resistance to antibiotics represents a global threat to public health. The larval excretions and secretions (ES) derived from necrophagous flies of the Calliphoridae family could configure a promising source to counteract their effects. Objective:.To compare the antimicrobial activity of native ES, ES greater and less than 10 kDa from Calliphora vicina and Sarconesiopsis magellanica (Diptera: Calliphoridae) Materials and methods: The bioassay was carried out using the turbidimetry technique and in the case of ES less than 10 kDa, the Minimum Inhibitory Concentration (MIC) was determined. Results: The ESn and ES less than 10 kDa of both C. vicina and S. magellanica showed potent antibacterial activity against three Staphylococcus aureus strains and four Gram negative bacteria, the ES less than 10 kDa being more effective than the ESn in the two species of flies evaluated. Furthermore, ES less than 10 kDa had the same effectiveness, except in the MIC trials when were evaluated, where it was observed that ES less than 10 kDa from S. magellanica were more potent in all bacteria evaluated except for S. aureus ATCC 25923. ES greater than 10 kDa did not inhibit the bacterial growth. Conclusions: These results validate, potentially, to these substances as an important source for the isolation and characterization of antimicrobial.