A total of three treatments, i.e., negative control group (group A), 4% Mentha piperita powder (group B) and 4% ethanol extract of mentha piperita (group C) were added to the diets of Nile tilapia, Oreochromis niloticus to investigate the effects of the respective treatments on the growth, haematological and biochemical indices. Fish (30 ± 10 g) were distributed at a rate of 13 fish per glass aquarium and two aquaria have been assigned for each treatment. At the end of the experiment (2 months) , results indicated that there was significant increase (p<.05) in the weight gain and specific growth rate of groups which fed diet enriched with 4% mentha piperita powder and groups which fed on diet enriched with 4% ethanol extract of mentha piperita when compared with control group. The recorded results of haematological and biochemical parameters included Hb, pcv, RBCs count, WBCs count, albumin, glucose, ALT, AST, uric acid, urea and creatinine and indicated no significant difference between different groups