Nine groups of in Tilapia nilotica fish, each consisting of 50 fish were used to assess the effect of pesticides on the haematological, biochemical and immunological parameters in fish. Four groups were injected with0,05 ml of staphylococcus aureus antigen, plus complete Freund's adjuvant, the first group (G1) was exposed to lindane treatment, the second group (G2) was exposed to dialdrin, the third (G3) was exposed to Diazinon and the fourth (G4) was exposed to malathion. Four other groups were not immunized, but injected with the adjuvant and exposed to the pesticides. The fifth group (G5) was exposed to lindane, the sixth (G6) was exposed to dialdrin, the seventh (G7) was exposed to Diazinon and the eigth (G8) was exposed to malathion. The ninth group (G9) was exposed to water without any pesticide treatment and served as controls. Both vaccinated and non-vaccinated groups was exposed to 1/10 LC50 of the tested pesticides. The results revealed that the mean total RBCs, WBCs counts , PCV, Hb, MCV, MCH, MCHC values were lower in vaccinated groups than in the groups exposed to the tested pesticides. The total protein, globulin and serum enzymes ALAT, ASAT values as well as macrophage phagocytic index and antibody titer were lower in vaccinated as compared to the non-vaccinated groups.