Since the last decade naturally occurring diarylheptanoids have been in the focus of scientific interest due to their various. beneficial biological effects. Besides the outstanding importance of the curcuminoids isolated from members of the Curcuma genus (Zingiberaceae), several different diarylheptanoids identified in Alnus species (Betulaceae) have been proved to possess notable pharmacological effects. Chemoprotective, neuroprotective, hepatoprotective, antiviral, antibacterial, antiinflammatory and antioxidant activities suggest their potential role in clinical practice. The aim of our study was the phytochemical investigation of the Corylus (Betulaceae) species native to Hungary: the Common hazel (Corylus avellana L.), the Turkish hazel (Corylus colurna L.) and the Filbert (Corylus maxima Mill.) in order to characterise their phenolic-profile. Although these plants have been used in traditional medicine for long time, literature data regarding their phytochemical composition is limited to the flavonoid and hydroxycinnamic-acid derivatives of C. avellana leaves. No previous studies have been published reporting the presence of diarylheptanoid compounds in any of the Corylus species. Soxhlet extraction with solvents of increasing polarity was performed on the bark and leaves of the mentioned three Corylus species. The phenolic-profile of the methanolic and ethyl acetate extracts was investigated by HPLC-DAD-ESI-TOF-MS and HPLC-DAD-ESI-MS/MS methods. Altogether 37 different phenolic compounds were detected in the extracts: twenty diarylheptanoids (1-20), nine flavonols (21-29) and eight other phenolics: caffeic and quinic acid derivatives and flavanones (30-37). The main compounds of the extracts were identified as myricetin- quercetin- and kaempferol-3-O-rhanmosides.