Anin vitroexperiment was conducted to investigate effects of supplementing oil or in combination with grape seed proanthocyanidin (PA) extract on true digestibility, ruminal fermentation and methane (CH4) emission in dairy goats. For this purpose, four non-lactating dairy goats were received an adapted diet containing concentrate and elephant grass (40:60, in DM) for 7 days. Animals were then collected rumen fluid before morning feeding to conduct batch in vitro fermentation. This study was carried out as a completely randomized design with 7 treatments and 4 replicates. A control diet consisted of concentrate and elephant grass at 40:60 while other 6 treatments were supplementation of 2.5% oil (either only soybean oil [S] or a mixture of soybean oil and tuna fsh oil [SF]) combined without or with grape seed proanthocyanidin extract (contained 95% PA [P]) at 0, 0.4 and 0.8% DM, corresponding to Ctrl, SP0, SFP0, SP0.4, SP0.8, SFP0.4 and SFP0.8, respectively. Treatment diets had no effect on pH, NH3-N concentration and in vitro true digestibility (P>0.05), however total VFA concentration at 48h incubation was greater in SFP0 compared to that in Ctrl (Punchanged when feeding either oil alone or in combination with grape seed PA extract (PMethane (CH4) concentration showed a strong drop in SP0.8 and SFP0.8 contrary to those in Ctrl and SP0 (P4 production in both SP0.8 and SFP0.8 related to Ctrl (Pthat feeding combination of grape seed PA extract at 0.8% DM with either soybean oil alone or a blend of soybean oil and tuna fsh oil at 2.5% DM strongly suppresses CH4 production without adverse effect on digestibility and ruminal fermentation in dairy goats.