Abstract: An experiment was conducted to study the effects of Thyme Methanol Extract (TME), on rumen methanogenesis in vitro. Different levels (0, 0.25 and 0.5 mL) of TME were incubated for 2, 4, 12, 16, 24, 48, 72 and 96 h in diluted ruminal fluid with a 100% forage diet (alfalfa) to evaluate their effects on rumen methane production. This experiment was carried out based on Complete Random Design (CRD) with three treatments and three replicates. Treatment A is 0 mL of TME and diet (control), Treatment B is 0.25 mL of TME and diet and Treatment C is 0.5 mL TME and diet. Result indicated that the methanol extract of thyme (0.25 and 0.50 mL) reduced methane production in all of the incubation times without 2 h (p<0.05).