Background: Reactive oxygen species (ROS) are implicated in various pathological conditions. Synthetic antioxidants have adverse health effects, while many medicinal plants have antioxidant components that can prevent the harmful effects of ROS. Objectives: This study quantitatively determined the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant properties of ethanol extract of the stem bark of Terminalia glaucescens (EESTG). Materials and Methods: The objectives were achieved based on in vitro assays. Data were analyzed by Sigma Plot (version 11.0). Results: Using gallic acid as the standard compound, TPC value obtained was 596.57 µg GAE/mg extract. TFC content of EESTG, determined as quercetin equivalent was 129.58 µg QE/mg extract. Furthermore, EESTG significantly (P < 0.001) displayed higher reducing power activity than the standard compounds (ascorbic acid and butylated hydroxytoluene [BHT]). Total antioxidant capacity assay, measured by phosphomolybdate method, was 358.33 ± 5.77 µg butylated hydroxytoluene equivalents [BHTE]/mg extract. β‑carotene‑linoleate bleaching method affirmed the potency of EESTG because of its significantly (P < 0.001) higher anti‑oxidant activity when compared with quercetin and BHT. Based on DPPH assay, EESTG displayed significantly (P < 0.001) higher activity than BHT, while the hydroxyl radical scavenging activities of BHT and quercetin significantly (P < 0.001) exceeded that of the extract, although EESTG still displayed a high level of activity obtained as 83.77% in comparison to 92.80% of the standard compounds. Conclusion: Findings from this study indicate the presence of promisingly potent phytoconstituents in EESTG that have the capability to act as antioxidants and free radical scavengers.