The qualitative and quantitative analysis of phenolic compounds of the methanol extract of Tunisian thornless form Opuntia ficus indica flowers was described. Reversed phase high-performance liquid chromatography UV photodiode array analysis detected four peaks at 320 nm, attributed to phenolic acids; three of them were quantified to 141 mg.kg(-1) of fresh plant material. Electrospray ionization mass spectrometer analysis detected 8 glycosylated flavonols at 350 nm, identified among 11 chromatographic peaks. The amount of flavonoids was 4980 mg.kg(-1) of fresh plant material, with isorhamnetin glycosylated derivatives as the main flavonoid components (55.1%), quercetin derivatives as the second (23.7%), and kaempferol derivatives as the third (8.4%).