The present study was designed to investigate the influence of dietary supplementation of Copper (I) nicotinate complex at different concentrations (30 and 60 mg/kg feed) for 4 weeks on the immune response and some biochemical parameters of Mugil cephalus fish vaccinated with Yersinia ruckeri bacterin. The relative level of protection against challenge with virulent strain of Yersinia ruckeri was also determined. The present findings indicated that, the using highest concentration of Copper (I) nicotinate (60mg/kg feed) was preferable for stimulation of hemopiosis which reflected on the significant increase of some tested hematological parameters. Both concentrations Copper (1) nicotinate complex had no adverse effect on liver cells which reflected on the unchanged activity of liver enzymes and increase the serum total protein, albumin and globulin. The increased lymphocytes percentage and serum globulin along the course of experiment was elevated phagocytic index and activity gave a strong evidence of the immunostimulant effect of copper (1) nicotinate complex in the levels of cell mediated and humeral immunity. This immunostimulant effects were dose dependant and