To determine the effects of Terminalia catappa extract (TCE) immersion on the survival and hematological profile of Betta sp, a group of fish was immersed in 500 ppm TCE and compared with the control group. After three days of immersion, survival, leukocyte (WBC), erythrocyte (RBC), hemoglobin (Hb), hematocrit (Hct), platelet (PLT), and differential leukocyte counts were compared between the two groups. Surviving fish from each group were then divided into three subgroups: subgroup without injection; subgroup injected with normal saline; subgroup injected with Aeromonas hydrophila. Survival, WBC, RBC, Hb, Hct, PLT, the percentage and number of lymphocyte, monocyte, and granulocytes post injection were evaluated for 48 h. The results showed that the survival of immersed fish was significantly higher than that in the control. No significant differences in the hematological profile were noted between the control and the immersed fish. The WBC of control subgroup (A. hydrophila injection) was significantly increased after 24 h. The fish immersed and injected with A. hydrophila had the highest PLT. The number of lymphocytes of all subgroups of fish was stable while the percentage of monocytes and granulocytes of the subgroups of immersed fish were increased. This finding suggested that 500 ppm of TCE is beneficial for improving survival, blood profile, and resistance to A. hydrophila.