Abstract: To investigate effects of dietary lysozyme supplementation on growth performance, immune-antioxidant capacity and antibacterial properties of GIFT tilapia (Oreochromis niloticus), basal diet or basal diet added with 18, 36, 54, 72 or 90 mg/kg lysozyme were formulated for a 60 days experiment. The results showed that the 54 mg/kg lysozyme addition group had the best growth and feed efficiency in which weight gain rate and protein efficiency ratio increased and feed conversion ratio decreased significantly compared with the control group (P0.05). lysozyme supplementation decreased hepatosomatic index with significant difference in 90 mg/kg group compared with the control group (P0.05). Spleen-somatic index was significantly lower in 36 mg/kg and 54 mg/kg groups compared with that of the control group (P0.05). Crude protein and ash content in whole body in 54 mg/kg group were significantly higher than that of the control group (P0.05). Lysozyme supplementation in 54 and 72 mg/kg group increased serum and liver superoxide dismutase and catalase activity but significantly decreased malondialdehyde content compared with the control group (P0.05). Liver lysozyme activity in 54 and 72 mg/kg group was significantly higher than that of the control group, while serum lysozyme activity in groups except L90 group was significantly lower than that of the control group (P0.05). Serum antibacterial test showed more resistance to Escherichia coli, Staphylococcus aureus, Aeromonas hydrophila, Vibrio alginolyticus in 54 and 72 mg/kg group compared with the control group but more sensitive to Bacillus subtilis with a 34.71% and 42.21% reduction, respectively. These results indicated that diet lysozyme supplementation (such as 54 mg/kg) can improve GIFT tilapia growth performance by regulating immune-antioxidant capacity of tilapia and improving serum antibacterial properties.