The effect of different concentrations of garlic (Allium sativum) supplement in fish diet on growth and haematological parameters of Clarias gariepinus fingerlings was investigated. Fish were separated into four experimental groups of 0% (controls), 0.5%, 1.0% and 3% concentrations of garlic in diet and fed at 3% body weight per day in a renewal static bioassay system. Garlic supplemented diet did not have any significant effect on weight gain of C. gariepinus when compared to fish in the control diet. However, final fish weight was significantly (P<0.05) higher than the initial fish weight in all concentrations of garlic in fish diet and in the controls. No significant (P>0.05) difference in total length was observed in fish fed different concentrations of garlic at the end of 12 weeks. An increase in total length was observed in fish with garlic supplemented diet over fish in the control diet. Fish fed different concentrations of garlic in diet showed slight differences in total length but did not significantly (P>0.05) differ from each other in total length. Fish in 0.5% garlic diet had higher weight gain and total length than fish in the rest of the treatment groups and the controls. Final white blood cell (WBC), red blood cell (RBC), packed cell volume (PCV), haemoglobin (Hb) were observed to be significantly (P<0.05%) higher than the initial counts in the treatment groups as compared to the controls. RBC, PCV and Hb were however, significantly higher in fish fed 0.5% garlic supplemented diets than other concentrations. Plasma protein was observed to increase significantly (P<0.05) only in fish fed 0.5% and 1.0% garlic in diet. This study has shown that 0.5% (0.5g/kg) garlic supplement in fish feeds elicited more increase in fish total length and volume of haematological parameters of C. gariepinus. Garlic inclusion in fish diet at 0.5% (0.5g/kg) concentration is therefore beneficial for use in aquaculture to enhance the disease resistant status of C. gariepinus.