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The present study was conducted to investigate the effects of dietary soybean isoflavones (SI) supplementation on growth performance, innate immune responses, hepatic antioxidant abilities, heat shock protein 70 (HSP70) gene expression and resistance to the pathogen Vibrio harveyi in Trachinotus ovatus. A basal diet was supplemented with SI at 0, 10, 20, 40, 60, 80 mg kg(-1) feed for 8 weeks. Significantly maximum weight gain (WG) and specific growth rate (SGR) were observed in treatment with 40 mg kg(-1) SI supplement (P < 0.05). Feed conversion ratio (FCR), feeding rate (FR) and survival rate were not significantly different among treatments. Fish fed a diet with 40 mg kg(-1) SI showed significant increase in plasma total protein content, complement 3 content, lysozyme activity as well as respiratory burst activity, but decrease in alanine aminotransferase and aspartate aminotransferase activities (P < 0.05). Increased plasma alkaline phosphatase activity, hepatic total antioxidative capacity, catalase activity and superoxide dismutase activity were also noticed in fish fed SI at 40 or 60 mg kg(-1) (P < 0.05). On the contrary, the lowest hepatic malondialdehyde (MDA) content was observed in fish fed SI at 40 mg kg(-1) (P < 0.05). Compared with the control, the relative level of HSP70 mRNA in fish fed SI at 40-80 mg kg(-1) were significantly increased, respectively (P < 0.05). After challenge with V. harveyi, significant higher post-challenge survival was observed in fish fed diets with 40-80 mg kg(-1) SI supplement than that in control group (P < 0.05). These results indicated that dietary intake containing SI could enhance the immune ability of fish and improve its resistance to infection by V. harveyi. Especially supplementation with 40 mg kg(-1) SI to the fish for 8 weeks showed remarkable improvement in the growth, non-specific immune responses, hepatic antioxidant abilities and HSP70 gene expression.