The aerial part of Rubus rigidus var. camerunensis (Rosaceae) is used to treat respiratory and cardiovascular disorders in the Cameroonian traditional medicine. The ethanol extract exhibited more potent antioxidant activity ($E_{max}s$ of 119% and 229% activity on DPPH and ${eta}$-carotene test) than aqueous extract. Bioactivity-guided fractionation of the ethanol extract based on free radical-scavenging assay (DPPH assay) afforded five flavonoid glycosides (four flavonol glycosides and an anthocyanin) and three glucosides of $19{alpha}$-hydroxyursane-type triterpenoid (two monomeric and one dimeric triterpenoids). The flavonoids were identified as kaempferol 3-O-(2"-O-E-p-coumaroyl)-${eta}$-D-glucopyranoside (1), kaempferol-3-O-${eta}$-D-glucopyranoside (astragalin, 2), kaempferol-3-O-${alpha}$-L-arabinofuranoside (juglanin, 3), quercetin-3-O-${eta}$-D-glucopyranoside (isoquercitrin, 4), pelargonidin-3-O-${eta}$-D-glucopyranoside (callistephin, 5). The three triterpenoids were $2{alpha}$, $3{eta}$, $19{alpha}$, 23-tetrahydroxyurs-12-ene-28-O-${eta}$-D-glucopyranosyl ester (nigaichigoside $F_1$, 6), $2{alpha}$, $3{eta}$, $19{alpha}$-trihydroxyurs-12-ene-23-carboxyl-28-O-${eta}$-D-glucopyranosyl ester (suavissimoside $R_1$, 7) as monomeric triterpenoids and coreanoside $F_1$ (8) as a dimeric triterpenoid. The flavonoids exhibited potent antioxidant activities (66 to 93.56% against DPPH radical) and they were also active on ${eta}$-carotene test. Coreanoside $F_1$ exhibited a 63% antioxidant activity, meanwhile the other two triterpenoids showed a weak activity. Three important facts on structure-activity relationship were observed: Compound 8, a dimeric triterpenoid glycoside, strongly enhanced antioxidant activity of its monomers, compound 3 with 3-O-${alpha}$-L-arabinofuranyl has much more potent activity than compound 2 with 3-O-${eta}$-D-glucopyranosyl, and antocyanin (5) is more potent than its corresponding flavonol glycosides.