Background. Phrynops geoffroanus is a small turtle that inhabits lakes, rivers, and streams throughout South America. The body fat of this animal is used as a folk medicine in Brazil for treating illnesses such as sore throats, ear aches, mumps, rheumatism, and arthritis. The present study evaluated the antimicrobial activity of oil extracted from Phrynops geoffroanus (OPG), determined its chemical composition, and discussed the implications of its use in traditional medicine. The OPG was obtained from the ventral region of this turtle using hexane as a solvent. The antimicrobial activity of OPG was tested against standard and multiresistance strains of bacteria and fungi and its composition was determined indirectly by analyzing the methyl esters of the component fatty acids. The OPG presented a clinically relevant antifungal activity against Candida krusei ATCC 6258 (MIC 128 µg/mL). When the OPG was associated with the antibacterial and antifungal drugs, was observed a synergistic effect when associated the OPG with the gentamicin against the strain Pseudomonas aeruginosa 22. Our results indicated that OPG has clinically relevant antifungal activity against C. krusei, and demonstrated synergetic antibacterial activity in combination with commercial antibiotics against Pseudomonas aeruginosa.