Five flavonoids, acacetin ( 1 ), secundiflorol I ( 2 ), mucronulatol ( 3 ), isomucronulatol ( 4 ), and isovestitol ( 5 ) were isolated, with the fractionation being guided by the brine shrimp lethality test (BST), from the ethanolic extract of the whole plant of Robinia pseudoacacia (Fabaceae). The