Abstract: We investigated the anaesthetic effect of eugenol at different mass concentrations on juvenile Siganus oramin with body mass of (4.83±1.30) g at natural seawater at temperature of (29.3±1.1) ℃. The results show that when the mass concentration of eugenol was 30−80 mg·L^–1, the anesthesia time reduced but the recovery time increased with the increase of mass concentration of eugenol. During the anesthesia, the respiratory rate of juvenile S. oramin increased at light anesthesia state, but decreased rapidly during deep anesthesia until the respiratory arrested due to excessive anesthesia. When the mass concentration of eugenol was 30−100 mg·L^–1, the juvenile S. oramin could reach Stage 4 anesthesia within 3 min and recovered less than 4 min with a survival rate of 100%. When the air exposure time was within 8 min, the recovery time slightly reduced with extension of air exposure time; when the air exposure time was longer than 8 min, the recovery time increased but the recovery rate decreased with the extension of air exposure time. It is indicated that eugenol, with advantages of fast anesthesia, short recovery time and high recovery rate, is an ideal anesthetic for juvenile S. oramin. The concentration of eugenol is suggested to be 30 mg·L^–1 in production, and the artificial operation time should not exceed 6 min after anesthesia. The anesthesia concentration should not exceed 80 mg·L^–1 even for faster anesthesia.