Plant extracts may be highly effective as natural dietary supplementation options to alternate the dietary antibiotics as growth promotors in ruminant diets. The current study was conducted to evaluate the dose response effects of the moringa (Moringa oleifera) leaf extract (MLE) as a natural alternative to monensin in sheep diets, on ruminal methane production (CH4), gas production (GP), nutrient degradability and fermentation parameters. The in vitro semi-automatic system of GP was used. The treatments were MLE added to a basal diet (consisted of 50 concentrate: 50 forage) at 0 (control), 50 (MLE low) and 500 (MLE high) mg/ kg dry matter, and the ionophore antibiotic monensin was added at 40 mg/kg dry matter. Abundant quantities of essential amino acids, monosaccharides, glycosides and benzene derivatives phytochemicals components were detected by the GC–MS analysis of MLE. The most effective treatments to decrease (P < 0.05) CH4 were monensin and MLE high, while only MLE high enhanced (P < 0.05) the overall mean of total volatile fatty acids (VFAs) concentrations compared to the other treatments and the molar proportion of acetate compared to monensin. A decline (P < 0.05) in protozoal count was observed by monensin, while such effect did not appear at other treatments. No significant differences were observed among the experimental treatments in the ruminal degradability, ammonia concentrations or GP. This study demonstrated efficiency of MLE as an effective natural intervention to monensin in sheep diets.