Abstract: In present study, the rumen fluid of Duolang Sheep was used as donator to assess the different additive amount（5%,10%, 15%, 20%, 25% and 30%） of grape skin on gas production of protein-enriched diet in vitro. The gas production（GP）,fermentation parameter（a, b, c）, p H values and organic matter digestibility（OMD） were determined to evaluate the nutritional value of grape skin as a feed resource and its optimal additive amount. The results revealed that the GP of the protein-enriched diet added with different amount of grape skin was increased with the extension of fermentation time, and it was significantly higher than that of control group（P0.05）. After fermentation for 72 hours, the highest GP was observed in protein-enriched diet added with 20% grape skin（90.50 m L, 72 h）, followed by 15%（85.67 m L, 72 h）. The lowest GP was observed in protein-enriched diet added with 5% grape skin（76.00 m L, 72 h）. At the end of the fermentation test, the highest OMD was obtained when the additive amount of grape skin was 10%, followed by 25% and 30%. The lowest OMD was obtained when the additive amount was 15%. The combined data showed that when 20% grape skin was added in protein-enriched diet, the relatively higher GP and OMD were obtained.