This study was conducted to evaluate the effect of Malva sylvestris leaf or stem extracts on in vitro fermentation kinetic, methane production and protozoa population of barley grain. Juice from leaves and stems were prepared by extraction from crushed materials. The extracts were then centrifuged at 454 × g for 15 min before use. The extracts were added at levels of 0, 25, 50 and 100 µL/250 mg barley incubated in 30 mL mixture of buffer and rumen fluid. Addition of both extracts increased the potential gas production (mL/200 mg DM), and constant rate (mL/h) but decreased the lag time (h) of barley grain (P < 0.01). Methane production from fermentation of barley grain decreased due to the addition of the extracts (P < 0.01). Methane reduction potential from fermentation of barley grain were 13.15, 7.30 and 13.28% when leaf extract was added at 25, 50 and 100 µL/250 mg barley, respectively. Corresponding values for similar levels of the stem extract were −1.94, 1.80 and 9.12%, respectively. Protozoa population in incubated barley grain medium with no extract was 9.94 × 10⁴/mL. The extracts particularly the extract from leaf resulted in much more protozoa reduction from barley grain fermentation (average values of protozoa population when leaf and stem extracts were added to barley grain incubation medium were 7.67 × 10⁴ vs. 7.85 × 10⁴/mL). The result of this study show M. sylvestris extract has some potential in improving the fermentation of barley grain