The present study was carried out to investigate the phytochemical composition and antioxidant activity of two Terminalia species (T. muelleri and T. myriocarpa). Antioxidant activity of the two Terminalia extracts was evaluated in vitro using DPPH, FRAP, and total phenolic content using rutin, iron sulfate, and gallic acid as reference materials. Polyphenol compounds of the two Terminalia leaves were investigated using HPLC and HPLC-MS/MS. It was shown that T. muelleri and T. myriocarpa leaves have high antioxidant activity. The polyphenols content of T. muelleri and T. myriocapa are 0.19 and 0.155 mg gallic acid/mg crude extract respectively, calculated as gallic acid. HPLC analysis of the two extracts revealed that the phenolic acids in T. muelleri and T. myriocarpa are predominantly free. The main compounds are cinnamic acid and gallic acid in all analytical fractions of both Terminalia species. LCMS/MS analysis of the ethyl acetate extracts of the two species identified the following flavonoid compounds such as rutin, quercetin, methyl gallate, and cafoylacetylhexoside in T. muelleri while rutin, quercetin, epigallocatechin gallate, and myricetin were identified in T. myriocarpa. The antioxidant activity observed by the examined extracts may be attributed to the high amount of polyphenols. These results support the medicinal and pharmaceutical importance of Terminalia species.