Abstract: Hematological indices of cobia, Rachycentron canadum, were investigated. The erythrocyte counts and leukocyte counts of cobia was 2.69?.86?06/mm3 and 1.50?.09?04/mm3 respectively. The hemoglobin content was 7.42?.22g/L,the erythrocyte osmotic fragility was 0.43?.07g% ,and the erythrocyte sedimentation rate was 1.18?.46mm/h. On the stained smears of peripheral blood, erythrocyte and thrombocytes, lymphocytes, neutrophils and monocytes, were recognized, but bsophilic granulocytes and ensinophilic granulocytes were not found. Some immature blood cells and direct dividing of erythrocytes could also be observed on the smears. The percentages of thrombocytes, lymphocytes, neutrophils and monocytes in total leucocytes, were 61.20?.30% , 16.60?.28% ,16.00?.61 % and 6.20?.90% respectively. The development of blood cells in liver,spleen, pronephros and mesenephros of cobia was studied. The results showed that the blood cells of cobia generates mainly in pronephros and mesenephros; spleen is another tissue for the generation of granulocytes; liver can generate lymphocytes and granulocyte; the generation of thrombocyte had not been observed in these four tissues.