The antiviral substance from the bud of Syzygium aromatica was purified by ether and ethyl acetate extraction and successive chromatography on Sephadex LH-60, LH-20, G-25 and Lichroprep RP-18. The purified antiviral substance was homogeneous and identified as eugeniin. Eugeniin shows antiviral activity against herpes simplex virus at a concentration of 10 microg/ml.