The chemical composition of Mangifera indica L. cv. “Kent” leaves was determined by HPLC-ESI-QTOF-MS/MS. Polyphenolic compounds characterized as benzophenone derivatives were the main components found in extracts (1, maclurin 3-C-(2-O-galloyl)-D-glucoside isomer; 2, maclurin 3-C-β--D-glucoside; 3, iriflophenone 3-C-β--D-glucoside; 5, maclurin 3-C-(2,3-di-O-galloyl)-β--D-glucoside; 6, iriflophenone 3-C-(2-O-galloyl)-β--D-glucoside; 7, methyl-iriflophenone 3-C-(2,6-di-O-galloyl)-β--D-glucoside) and xanthones (4, mangiferin and 8, 6-O-galloyl-mangiferin). The estrogenic and antioxidant effects of aqueous extracts from Mangifera indica L. cv. “Kent” leaves on ovariectomized rats were determined by uterotrophic assay and malondialdehyde (MDA) levels in erythrocytes, bone, liver, and stomach. We conclude that the polyphenolic compounds from extracts act as exogenous antioxidant agents against oxidative damage in ovariectomized rats.