The hematology examination be able to descript the health of fish. The aim of this research was to study leukocyte and differential counting leukocyte in Carp (Cyprinus carpio Linn) after infected by Aeromonas salmonicida. P0 was a control group, not infected with Aeromonas salmonicida. P1, P2, and P3 group was infected by Aeromonas salmonicida through different doses, 10 5 cell/ml, 10 6 cell/ml, 10 7 cell/ml. Three days after infection, blood samples were obtained from Punctie Vena Caudal which deposited into EDTA tubes. Total number leukocyte and differential counting leukocyte analyzed were carried out with the collected blood samples. Data were analyzed with ANOVA (Analysis of Variant) then followed with Duncan's multiple range test significance level of 5%. The results showed there was significant increase (p<0.05) in the number of leukocytes compared with control (P0). There was significant increase (p<0.05) in the number of neutrophils and decrease in the number of eusinophils, lymphocytes and monocytes. The number of basophils were not significant decrease (p<0.05).