This study evaluated antioxidant activities and haematological effects of methanol extract of Asystasia gangetica leaves (MEAG) on monosodium glutamate (MSG) treated rats. Forty-two male Wistar rats randomly distributed into 7 groups (n=6) were used for the study. Groups 1-3 were the normal control, MSG control, and positive control respectively whereas groups 4-5 were the extract controls, and groups 6-7 were the curative groups. All the treatments were administered orally and standard analytical methods were used for analyses. The results showed that MEAG is a rich antioxidants source and contains phenolics, flavonoids and beta-carotene in high concentrations. The extract showed concentration-dependent increases in ferric reducing antioxidant power, DPPH (2,2-diphenyl-1-picrylhydrazyl) and nitric oxide radicals scavenging activities but relatively lower than their respective controls. The MSG administration caused significant (P<0.05) reductions in the glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) activities but significantly (P<0.05) increased the malondialdehyde (MDA) concentrations in the MSG control rats. The MSG administration also caused significant (P<0.05) reductions in the haemoglobin (Hb) concentration, packed cell volume (PCV), red blood cell (RBC) and white blood cell (WBC) counts of the MSG control relative to the normal control. Treatment with MEAG significantly elevated GPx, SOD, and CAT activities; haematological indices and significantly reduced MDA levels in the extract controls, and curative groups treated with a high dose of MSG. These findings show that methanol extract of A. gangetica leaves is rich in antioxidants that could prevent oxidative stress and improves the haematological profile of MSG treated rats.