The study investigated the effect of Citrullus lanatus juice extract on haematological parameters and antioxidant of male Wistar Albino Rat. Thirty (30) male Wistar rats weighing 150-200g were randomized into four groups and were treated orally within Citrullus lanatus extract for twenty one days. Group 1 (control) received normal fluid and water only, Group two (low dose) received 2.5ml/kg, Group three (medium dose) received 5ml/kg and Group four (high dose) received 10ml/kg of the extract for a period of 21days. At the end of the experiment the rats were sacrificed and the blood sample was statistically analyzed using ANOVA, followed by Duncan multiple range test. (P<0.05) were considered statistically significant. The finding showed there was a significant effect on the antioxidant. In malondialdehyde, there was a significant increase in the groups that were administered with extract at low dose (2.58±0.10) when compared with the control group (2.36±0.12), medium dose (2.42±0.06) and high dose (1.98±0.23). There was significant difference when compared control group with high dose. In catalase, there is significant difference between the treated groups at low dose (2.95±0.48), medium dose (3.13±0.37) and high dose (2.03±0.20). There is significance increase in Superoxide when in medium dose was compared with control group. Also there is significant differences (p<0.05) in the groups administered with C.lanatus extract at low dose (1.59±0.11), medium dose (1.36±0.11) and high dose (1.55±0.04). Finally there was no significant difference in PCV at low dose (46.20±2.48), medium dose (45.20±0.80), and high dose (44.00±1.52) when compared with the control (45.20±1.28). There was significant increase in basophil when medium dose (0.60±0.24) when compared with low dose (0.00±0.00) and high dose (0.00±0.00). This result suggest that the administration of Citrullus lanatus has no effect on PCV, Haemoglobin but rather decreased body weight.