Kouazounde, J. B., Gbenou, J. D., He, M., Jardim, T., Jin, L., Wang, Y., Beauchemin, K. A. and McAllister, T. A. 2015. Effects of essential oils from African basil on fermentation of Andropogon gayanus grass in the Artificial Rumen (RUSITEC). Can. J. Anim. Sci. 95: 425-431. Essential oils (EO) from African basil (Ocimum gratissimum) have shown the potential to modify rumen microbial fermentation and reduce ruminal methane production from grass forages in in vitro batch cultures. However, it is not known whether the effects of EO on rumen microbial fermentation attenuate over time. The objective of this study was to examine the effects of African basil EO at 0 (control), 100, 200 and 400 mg L^-1 incubation medium on microbial fermentation and methane production in the Rumen Simulation Technique (RUSITEC) using Andropogon gayanus grass as a substrate. African basil EO quadratically affected (P<0.05) methane production gas production and the pH of fermenter liquid. Total volatile fatty acid (VFA) production was linearly decreased (P<0.05) by African basil EO along with a shift in VFA profile towards less propionate and more acetate and butyrate. African basil EO quadratically altered (P<0.05) apparent dry matter, neutral detergent fiber digestibility, ¹⁵N incorporation into total microbial protein and the total production of microbial protein. This study confirms that EO from African basil quadratically affected methane emissions arising from the ruminal fermentation of A. gayanus grass mainly by reducing overall digestibility of the forage.