Introduction: Moringa (Moringa oleifera) is a plant found in many regions. Its extracts, especially of leaves are a rich source of fibre, proteins and micronutrients including iron, thus potentially used for haematological applications including iron deficiency anaemia affecting approximately one-third of the global population. Objectives:To systematically review the effect of M. oleifera on haematological parameters Methods: Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines were followed. PubMed, Cochrane library, Agricola, CINAHL and EMBASE databases were searched. Selection of articles were done in with three screening questions by two independent reviewers intervened by a third, resolving conflicts. Human studies on Moringa with relevant outcomes were included. Risk of bias assessment was done with Grading of Recommendations Assessment Development and Evaluation (GRADE) Criteria. Heterogeneity was assessed and results were narratively synthesized without meta-analysis. Registration from International Prospective Register of Systematic Reviews (ID: CRD42020181432) was obtained.Results: Following de-duplication, there were 215 articles. Eight studies on M. oleifera leaf extracts, covering nine outcomes were included (four studies on children below 2 years and two each on pregnant women and reproductive & postmenopausal women). Among children under 2 years, mean improvement in haemoglobin level ranged between 0.31-2.6 g/dl, with a reduction of the prevalence of anaemia by 53% (95% CI=35.1, 72.0; p<0.001). Haemoglobin level among anaemic women in reproductive ages showed an improvement with a mean difference (MD) of 0.794 (SD=0.81) (p<0.05) in the interventional group and of 0.644 (SD=0.83) in the control group. Postmenopausal women showed a significant improvement of 17.5% in haemoglobin compared to baseline (p≤0.01). Two studies showed improvements in ferritin levels with an MD of 29.378 ng/mL (SD=42.48; p=0.012) among anaemic women and 31.9 (SD=23.8) among children under 2 years. One study showed an improvement in the MD of erythrocyte count (0.482; SD=2.26), hematocrit (0.947; SD=4.56), MCV (0.635; SD=11.22), MCH (1.312; SD=4.94), MCHC (2.459; SD=2.86) and RDW (1.4; SD=2.07) compared to the control group. Among the pregnant women, improvements in both MCH and MCV were statistically significant in the intervention group (p<0.05). Conclusions & Recommendations:Moringa leaf extracts as a natural supplement is seemingly useful for improving haematological parameters, especially the haemoglobin level among children and female adults.