The effects of injectable Tunceli garlic oil (Allium tuncelianum) on serum response of rainbow trout were examined. Influence of intraperitoneal (i.p.) injection administration of Tunceli garlic oil (TGO) was evaluated on some immunological factors of rainbow trout. Fish weight 40 g were i.p. injected TGO at doses of 1% and 10%. Serum lysozyme activity, bactericidal activity, myeloperoxidase, protein and immunoglobulin levels were measured on days 3, 7, 14 and 21 after the TGO administration. All the immune parameters assayed remained affected when TGO was i.p. administered. Serum bactericidal activity was consistently achieved by immunizing fish with TGO. Levels of serum myeloperoxidase activity were increased in the groups of fish injected with TGO. Myeloperoxidase and bactericidal activities peaked at 14 and 21 days post-injection, respectively. Lysozyme activity was significantly increased throughout experiment in the all groups. Total protein and immunoglobulin levels increased in the 21 days post-injection although no statistically significant differences. In conclusion, these results suggest that there are functionally effects of TGO on the immune mechanisms of rainbow trout.