A new pholoroglucinol derivative named eucalyptone G (4) together with nine known compounds (1-3, 5-10) were isolated for the first time from the ethyl acetate fraction of the bark of small twigs of Eucalyptus globulus Labill. Their chemical structures were established on the basis of physical, chemical and spectroscopic methods 1D (1H and 13C) NMR and 2D (COSY, HMQC and HMBC) NMR in addition to mass spectrometry and comparison with literature data. Eucalyptone G displayed antibacterial activity against Bacillus subtilis, Staphylococcus aureus and Escherichia coli.