Endophytic fungi represent a compelling assemblage of microorganisms that inhabit plant tissues without inflicting any discernible detriment to the host organism. They foster a symbiotic association with their host plants, frequently conferring advantages such as augmented growth, enhanced resilience to stressors, and safeguarding against pathogens. Dillenia indica is a medicinal tree of Dilleniaceae. This study aims to isolate and identify the fungi growing as a contaminant in leaf callus. For the identification, both morphological observation and molecular methods were used. The presence of secondary metabolites in different fungal extracts were observed by FTIR and High-resolution accurate mass spectroscopy (HRAMS) methods. Different biological activities (antioxidant, antibacterial and antitumor) of fungal extracts were assessed. For callus initiation, leaf tissues of Dillenia indica were inoculated on Murashige and Skoog's medium supplemented with BAP (1mgl-1) and NAA (1mgl-1) plant growth regulators. To raise pure cultures of endophyte, fungal hyphae were isolated from the contaminated cultures and were grown on Potato Dextrose Agar medium. For molecular identification, genomic DNA (gDNA) was isolated from fungal mycelia. Internal transcribed spacers (ITS1 and ITS4) were used to amplify the conserved ITS region of the fungal gDNA. Previously deposited sequences in the Gene bank were used for the identification and making of phylogenetic tree. Antioxidant, antibacterial and anticancer potential of fungal extracts were studied. The endophyte was identified as Aspergillus flavus. FTIR study showed the presence of diverse types of secondary metabolites in fungal extract. A significant presence of phenolics, flavonoids, terpenes, steroids, etc. was observed by High-resolution accurate mass spectroscopy analysis (HRAMS) of fungal extract. Endophyte extract prepared in chloroform showed both antioxidant (IC₅₀ 430.23) and antibacterial (maximum inhibition of E. coli:15 ± 0.62 mm) potential compared to other solvents. Cell viability decreased at high concentrations of endophyte extract prepared in chloroform and ethyl acetate solvents. Fungal extract prepared in ethyl acetate showed considerable cytotoxicity and growth inhibition of DL tumor cells. In the present study, isolated endophyte of Dillenia indica showed high occurrence of secondary metabolites. Fungal extracts showed antioxidant, antibacterial and antitumor activities. As, endophytes are remarkable source of active constituents, there is a great need to explore such endophytes. Their extensive studies are required to develop an alternative of plant less production of valuable compounds.