The purpose of this study is to compare the biological activities and the phytochemical contents of Terminalia arjuna's different parts (leaves, fruits, and bark). Firstly, phytoconstituents (tannins, phenols, and flavonoids) in the methanol extracts were determined qualitatively and quantitatively. Followingly, the antioxidant, anti-inflammatory, and antimicrobial capabilities of T. arjuna's leaves, fruits, and bark were evaluated. The antioxidant activity was measured using four assays: 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, hydrogen peroxide (H2O2) scavenging, ferric reducing antioxidant power (FRAP), and total antioxidant capacity (TAC), while the anti-inflammatory activity was determined using Human-RBCs membrane stabilisation assay. The antimicrobial potential and MIC were measured against eight selected microorganisms using the agar well diffusion assay and the agar dilution method, respectively. All extracts demonstrated strong antioxidant and anti-inflammatory characteristics. Leaves methanol extract exhibited the highest antioxidant activity with IC50 (for DPPH and H2O2), FRAP and TAC values of 12.20 µg/mL, 20.60 µg/mL, 3.21 mMol Fe+2/g and 62.74 mg GAE/g respectively. The highest protection against HRBCs lysis was 95.71% for 5 µg/mL dose of leaves methanol extract and 98.22% for 10 µg/mL dose of fruit methanol extract. The antimicrobial activities of the extracts differed clearly. The maximum activity of leaves, fruits, and bark methanol extracts was against Bacillus subtilis (MIC=39.06 µg /mL), Klebsiella pneumonia (MIC= 156,25 µg /mL), and Proteus vulgaris (MIC = 39.06 µg /mL), respectively. These results suggest that T. arjuna's leaves have more potential beneficial effects than bark and fruits, but future in-vivo and clinical research is required.