Introduction: Cinnamomum mercadoi is a medicinal tree endemic to the Philippines. Cinnamomum species have been extensively studied for their endophytic fungi with pharma cological importance. This study aims to isolate and evaluate the antibacterial activity of endophytic fungi associated with the bark of C. mercadoi. Materials and Methods: Endophytic fungi were isolated from surface sterilized bark samples aseptically. The pure isolates were identified through their morphological characteristics. Agar plug diffusion assay was employed in the primary screening of their antibacterial activity against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa. Four active endophytes were fermented and extracted with ethyl acetate (EtOAc). The antibacterial activity of the EtOAc extracts was screened using the disk diffusion assay. The minimum inhibitory activity (MIC) was evaluated using the microdilution method. Results: Twelve (12) endophytes were isolated from the bark of C. mercadoi. All endophytes exhibited antibacterial activity on at least one of the test pathogens. However, only two of the four endophytes subjected to the secondary screening showed wide-spectrum activity and inhibited the growth of all test bacteria. Fusarium sp. 2 was identified to have the most promising activity with MIC values ranging from 2.1 -4.2 mg/mL. Conclusion: C. mercadoi harbors endophytes, particularly Fusarium sp. 2, which possess antibacterial activity and thus a potential source of antibacterial compounds. endophytic fungi, particularly those isolated from medicinal plants for their potential as source of new antibiotics. [8][9][10] Several Cinnamomum species has been studied for their associated endophytes because of their promising antibacterial activity.11-13 Moreover, active compounds have been isolated from endophytic fungi associated with this species. Cinnamomum zeylanicum, collected from Honduras, was the host of a novel endophyte Muscador albus which was reported to contain volatile organic compounds with antimicrobial activities.14 Antimycobacterial compounds were isolated from Annulohypoxylon ilanense, an endophyte of a Cinnamomum species from Taiwan. 15 Cinnamomum mercadoi (Lauraceae) is a tree endemic to the Philippines. It is traditionally used as expectorant and for the treatment of digestion problem and tuberculosis. 16,17 Biological studies of C. mercadoi had shown that its crude extract exhibited analgesic, antimicrobial, antioxidant and antidiarrheal properties. [17][18][19] No previous study on its endophytic fungi has been reported to the best of our knowledge. In this study, we have isolated 12 endophytic fungi and screened them for their antibacterial activity. An Ascomycete isolate, Fusarium sp. 2, is being reported to have a broad spectrum and promising antibacterial activity. MATERIALS AND METHODS Sample CollectionBark samples were collected from a healthy Cinnamomum mercadoi tree in Barangay Patag, Baybay, Leyte, Philippines (10.74 °N, 124.79°E,31.5 m elevation) i...