An in vitro experiment 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 fish 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, SP_0.4, SP_0.8, SFP_0.4 and SFP_0.8, 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 (P0.05). Methane (CH₄) concentration showed a strong drop in SP_0.8 and SFP_0.8 contrary to those in Ctrl and SP₀ (P4 production in both SP_0.8 and SFP_0.8 related to Ctrl (P4 production without adverse effect on digestibility and ruminal fermentation in dairy goats.