A vast and unexplored source of diverse and unique compounds and biological properties is provided by the mangrove fungi. The primary goal is to investigate the biological effects of secondary bioactive compounds produced by endophytic fungi that reside in Aegiceras corniculatum bark, focusing on their antioxidant, alpha-glucosidase inhibitory, and antimicrobial properties. Seven distinct strains of endophytic fungi were isolated, of which three particular strains (ACSF-1, ACSF-3, and ACSF-5) were selected for further examination. These strains were cultivated in potato dextrose broth (PDB) and underwent extraction using dichloromethane (DCM) and ethyl acetate (EtOAc). In the DPPH assay, the fraction ACSF-3 of the DCM showed a good IC₅₀ value of 239.88 µg/mL, whereas the ascorbic acid IC₅₀ was 15.985 µg/mL. Additionally, the crude extract ACSF-3 exhibited the highest levels of total phenolic content (89.89 mg GAE/g), total flavonoid content (288.52 mg QE/g), and total tannin content (53.85 GAE/g). To evaluate antihyperglycemic activity, the ACSF-3 n-Hexane fraction, which showcased the highest efficacy with a value of 0.91 µg/mL. The extracts of ACSF-1 and ACSF-3 demonstrated significant zones of inhibition against Escherichia coli, with sizes reaching up to 16 and 12 mm, respectively, and ACSF-5 displayed the highest zone of inhibition against Staphylococcus aureus.