Two novel bioactive monotetrahydrofuran acetogenins, annoreticuin (1) and isoannoreticuin (2), have been isolated from the leaves of Formosan plant Annona reticulta L. (Annonaceae). The plane structures of these two new compounds were elucidated on the basis of 1 H and 13 C nmr data and by mass spectrometry. These two compounds showed selective cytotoxic activities for certain human tumor cell lines