This study aimed to analyze the blood profile of tilapia (O. niloticus) on fortified feed with E. cottonii seaweed flour. This research was conducted for 60 days at the Laboratory of the Aquaculture Study Program, Faculty of Agriculture, University of Mataram. The method used was Completely Randomized Design (CRD) experiment with four treatments and three replications, namely P1 (without E. cottonii flour), P2 (E. cottonii flour 4%), P3 (E. cottonii flour 8%), P4 (E. cottonii flour 12%). The parameters measured were hematocrit, hemoglobin, erythrocytes, leukocytes, absolute weight, absolute length, SR and water quality including temperature, DO, and pH. Statistically analyzed at 5% significance level with 95% confidence level using ANOVA analysis and further test using Duncan's Multiple Range test. The results showed that the hematocrit value ranged from 10.67-13.67%, hemoglobin ranged from 5.1-9.1G%, erythrocytes ranged from 2.2x106-9.9 x106 cells/mm. leukocytes ranged from 11.4 x104-17.6 x104 cells/mm, absolute weight ranged from 16.26 -18.6 g, absolute length ranged from 5.08±0.50-5.91±0.27cm and survival (SR) ranged from 86.7±11.55-93.3±5.77%. Measurement of water quality, temperature 28-28.8, DO 6.8-7.5, and pH 7.43-7.99. The addition of different E. cottonii flour to tilapia feed affected hemoglobin, erythrocyte, leukocyte and growth levels, but did not affect hematocrit levels and survival rates. Supplementation of E. cottonii flour to a concentration of 12% in feed can increase hemoglobin, erythrocyte, and leukocyte levels so as to support better growth performance of tilapia