Abstract: This study was undertaken to determine the effect of dietary chromium supplementation on humoral antibody response and some blood constituents in hybrid tilapia fish (Oreohromis niloticus x O. aureus). Cr-yeast or Chromic Oxide (Cr2O3) were added to fish feed at the rates of 1 or 2 mg kg-1, while control fish received unsupplemented diet. Three hundred and forty fish (Avg. weight 37.8 g) were randomly assigned to 5 feeding regimens with two replicates each. Each replicate was reared separately. The fish were immunized with Sheep Red Blood Cells (SRBCs) at 0 day and re-immunized at 30 days of the experiment to determine primary and secondary humoral antibody responses, respectively. Blood samples were collected from 15 fish/replicate at 0 and 25 days to determine blood plasma constituents and at 5 days intervals during primary and secondary immunization up to 50 days to determine anti-SRBC antibody titers. The results shown decreased plasma glucose and increased plasma cholesterol concentrations at 25 days compared to 0 days in all groups. Increased triglyceride levels was noted in fish receiving Cr2O3 (1 mg kg-1) and decreased albumin: globulin ratio in those receiving Cr yeast (2 mg kg-1) at 25 days (p<0.05). No significant changes were observed in total protein, albumin and total globulin concentrations due to either Cr treatment or feeding duration. Anti-SRBC antibody titers were significantly higher in Cr-supplemented groups versus control, with highest titers in fish receiving 2 mg kg-1 Cr-yeast supplement during secondary immunization. These findings indicate that the inclusion of Cr in the feed significantly augments humoral antibody response of tilapia.