This study was aimed to investigate the effect of various doses of jeruju leaf extract administered through feed on the blood parameters of tilapia, including erythrocyte count, leukocyte count, and differential leukocyte count and to determine the dose effectively affected the blood parameters of tilapia. Jeruju is a type of herbaceous plant or phytopharmaca which has the potential to enhance fish immunity. This plant is mostly found in coastal areas. The study was conducted from July to August 2018 in the Laboratory of Tanjung Balai Polytechnics (extract preparation), Blood Laboratory of Kisaran (blood examination) and Dusun IV in Pahang Village, Talawi Subdistrict, Batu Bara Regency (research location). The research method applied was the experimental method with Completely Randomized Design (CRD) consisted of four (4) treatments and six (6) replications, namely A (0 g/kg), B (8 g/kg), C (10 g/kg), and D (12 g/kg). The blood parameters of tilapia which included leukocyte count, erythrocyte count, and the percentage of lymphocytes, neutrophils, and monocytes were examined on the 0th, 7th and 14th day of the study. The administration of jeruju leaf extract resulted in a significant effect on leukocyte count, erythrocyte count, and lymphocyte percentage (P<0.05), but did not significantly affect the percentage of neutrophils and monocytes.