In this study, control (0), 50, 100, 200, 400, 800 and 1000 mg $L^{-1}$ gingeressential oil (GEO) (Zingiber officinale Roscoe) was added to rumenliquid (RL). Then, the effects of the GEO added to the RL In vitro gasproduction, organic matter digestibility (OMD), metabolisable energy(ME), rumen fermentation parameters and methane ($CH_4$) productionwere examined on these samples. It was determined that the addition ofthe GEO to RL decreased the in vitro gas production of Trifolium pratensehay (TPH), the OMD and ME contents, total volatile fatty acids (TVFA),acetic acid (AA), propionic acid (PA), butyric acid (BA) and other volatilefatty acids (OVFA) (P<0.05). Moreover, it was determined that while theproductions of carbon dioxide (CO2), CH4 and ammonia nitrogen (NH3-N) decreased, the ratios of the rumen pH and AA/PA increased (P<0.05)depending on the increase in the dose of GEO. In conclusion, it wasdetermined that the GEO dose which had the highest negative effect onthe in vitro gas production, the rumen fermentation, the nutrientdigestibility, the $CH_4$ and the $CH_2$ production was 1000 mg $L^{-1}$. It wasconcluded that since high doses of GEO affect rumen fermentation anddigestion of feeds negatively, it would be appropriate to use 200 mg $L^{-1}$