A new unusual eugenyl-O-β-D-(6'-sulphonylglucopyranoside) and 17 polyphenols have been isolated from the leaves of Lannea acida and Lannea welwitschii. The structures of the compounds were established using NMR and HR-ESI-MS spectroscopic analysis. Six compounds namely myricetin 3-O-β-D-arabinofuranoside 1, myricetin-3-O-β-D-glucuronic acid 2, myricetin-3-O-β-D-xylofuranoside 3, myricetin 4, mearnsetin 5, myricetin-3-O-β-Dgalactopyranoside 6, were isolated from L. welwitschii. Twelve others including the new eugenyl-O-β-D-(6'-sulphonylglucoside) 7, myricetin-3-(6''-galloylgalactoside) 8, quercetin-3-O-β-D-glucuronic acid 9, quercetin-3-O-β-D-glucopyranoside 10, (-)-epigallocatechin-3gallate 11, (-)-epicatechin-3-gallate 12, myricetin-3-O-α-L-rhamnopyranoside 13, myricetin-3-O-β-D-glucopyranoside 14, 3,4,5-trigalloylquinic acid 15 and (-)-epigallocatechin 16, quercetin-3-(6''-galloylglucopyranoside) 17 and (-)-epicatechin 18 were obtained from Lannea acida. The antioxidant activity of 2, 4, 5, 10, 11, 12, 13, 14, 17 and 18 were evaluated by the DPPH (2, 2'-diphenyl-1-picrylhydrazyl) free radical-scavenging and CUPRAC method. Others due to their inadequate quantities were not evaluated. Compound 18 (IC50 7.8 ± 0.1 µg / mL), 4 (IC50 18.6 ± 4.5 µg / mL), 2 (IC50 20.0 ± 0.1µg / mL) and 13 (IC50 20.0 ± 0.9 µg / mL) showed better activity than the controls, ascorbic acid (IC50 23.17 ± 2.02) and quercetin (IC50 31.67 ± 2.88 µg / mL). This is the first report of the isolation of eugenyl-O-β-D-(6'sulphonylglucopyranoside. The seventeen (17) known compounds were reported for the first time in L. welwitschii and L. acida. Future studies would involve the anti-inflammatory and anticancer activities of these compounds.