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 diet) for 4 weeks On the immune response and some biochemical parameters of Big head carp fish (Japanese Carp Puntius goionotus) (Bleeker) vaccinated against Yersinia ruckeri bacteria. The survival rate against challenge with virulent strain of Yersinia ruckeri was also determined. The present findings indicated that, fish supplemented with copper (I) nicotinate showed a significant increase in the of Hb, PCV, lymphocytes, monocytes, basophils, eosinophils and  total percentages leukocytic count. However, the percentage of neutrophils was decreased significantly. Consequently, phagocytic activity and index were increased significantly. Both concentrations of the used copper nicotinate had no adverse effect on liver functions which reflected on the unchanged activity of liver enzymes and the increase in both serum total protein and albumin. Moreover, the significant increase of serum globulin was also recorded. The increased lymphocyte percentage and serum globulin along with increased phagocytic index and activity gave a strong evidence of the immunostimulant effect of copper nicotinate in the level of cell mediated and humeral immunity. This immunostimulant effect was dose dependant and confirmed by the increase in both antibody titer and relative Ievel of protection against the injected virulent strain of Yersinia ruckeri.