An investigation of the hepatoprotective and antioxidant activities of the chloroform, ethyl acetate and n-butanol fractions of the leaves of Albizia lebbeck L. was performed. The first two fractions expressed the best results regarding the suppression of the increased levels of plasma amino-transferases and alkaline phosphatase in liver-damaged mice (after intoxication with CCl4) compared with silymarin and the significantly increased GSH content of alloxan- induced diabetic rats compared with vitamin E (tests and reference drugs were orally administered). The bioactive fractions of Albizia lebbeck L. were subjected to chromatographic analysis to investigate their phenolic contents using a HPLC-PDA-ESI-MS/MS technique in the negative ion mode. The results constitute the first report of the presence of seven compounds in the genus Albizia, three of which were identified as 3-O-caffeoylquinic acid, cafeic acid, myricetin; four other flavonoids (in mg 100 g-1 dry powder ± SD), myricetin 3-O-rhamnoside (0.129 ± 0.0052), quercetin 3-O-dideoxypentoside (0.011 ± 0.001), kaempferol 3-O-glucoside (0.015 ± 0.002), quercetin 3-O-dihexoside (0.138 ± 0.002); quercetin 3-O-rutinoside at a level of 0.135 ± 0.004; and the aglycones quercetin, luteolin and kaempferol. Method validation was performed, providing an analytical technique that can be used to detect trace amounts of the identified compounds in Albizia extracts with rapid sample preparation.