The present study investigated the effects of dietary Spirulina platensis supplementation on growth performance, hematological and serum biochemical parameters, hepatic antioxidant status, immune responses and resistance to the pathogen infection in Coral trout Plectropomus leopardus. The fish were fed for 8-week with diets containing different levels of S. platensis: 0% (C), 2% (SP2), 4% (SP4), 6% (SP6), 8% (SP8) and 10% (SP10) as treatment groups, followed by a Vibrio harveyi infection test for 14 d. The study indicated that dietary supplementation with Spirulina platensis could significantly improve growth performance, and the highest weight gain rate (WGR) and specific growth rate (SGR) were observed in group SP10 (P < .05). Red cell count (RBC), white cell count (WBC), hemoglobin (Hb) and total antioxidant capacity (T-AOC) in the S. platensis supplemented groups were significantly higher than those of group C (P < .05). However, the levels of cholesterol, triglyceride and malondialdehyde (MDA) contents, and superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities decreased with the increasing of dietary S. platensis levels. Compared with group C, the lysozyme (LYZ) and respiratory burst activities (RBA), and immunoglobulin (Ig) and complement contents in group SP4, SP6, SP8 and SP10 increased significantly than those of group C respectively (P < .05). After challenge with V. harveyi, the survival rate in group SP4, SP6, SP8 and SP10 was significantly higher than that of group C, and the highest survival rate was in group SP10 (P < .05). These results indicated that P. leopardus fed a diet supplemented with S. platensis (especially at 10%) could significantly promote its growth performance, improve its hepatic antioxidant status, and enhance its immune ability and resistance to V. harveyi infection.