Abstract: This study was conducted to investigate the effects of shading during the grain filling stage on the nutritive value and in vitro digestibility of “Yangmai 15” wheat straw. Three shading levels (0%, 50% and 66%) and three shade duration periods (2, 4 and 8 days) were compared. At harvest, the wheat straw was collected and stored for analysis of chemical composition and in vitro digestibility and fermentation characteristics. For in vitro fermentation, rumen fluid was collected from 4 Boer goats with permanent rumen fistulas. Bottles containing 10 mL rumen fluid and 50 mL media with 1 g wheat straw as substrate were incubated at 39℃ for 72 h. Gas production was measured throughout the fermentation and samples were collected for analysis of pH, in vitro digestibility and volatile fatty acids (VFA) at the end of fermentation. The results showed that shading level and period significantly affected the crude protein (CP) content, neutral detergent soluble (NDS) and neutral detergent fiber (NDF) (P<0.05) with no interaction between shade level and shade period. When the shade level increased from 0% to 66%, CP and NDS decreased significantly from 3.06% to 2.35%, and 23.97% to 20.46%, respectively (P<0.05), while NDF increased significantly from 76.03% to 79.54% (P<0.05). Increasing the shading period from 2 to 8 days decreased CP and NDS significantly; 3.11% to 2.51%, and 23.09% to 21.43%, respectively (P<0.05), while NDF increased significantly from 76.9% to 78.6% (P<0.05).Shade level and shade period significantly affected the neutral detergent fiber digestibility (NDFD) (P<0.05) but no interaction was observed. With increasing shade level dry matter digestibility (DMD), NDFD and acid detergent fiber digestibility (ADFD) decreased significantly from 40.33%, 40.82% and 36.56% to 35.20%, 36.03% and 33.36%, respectively (P<0.05). With increasing shade duration NDFD decreased significantly from 38.88% to 36.94% (P<0.05). Both shade level and shade duration significantly affected gas production (P<0.05) and an interaction between them was observed (P<0.05); gas production decreased significantly from 131.64 mL to 120.96 mL, and 130.46 mL to 121.22 mL with increasing shade level and duration, respectively (P<0.05). The concentration of VFA in the cultures showed that shade level significantly affected TVFA concentrations, butyrate and the acetate/propionate ratio (A/P) (P<0.05), but shade duration had no effect on these traits. With increasing shade level the concentrations of TVFA and butyrate decreased significantly from 57.04 mmol/L to 51.25 mmol/L and 5.18 mmol/L to 4.32 mmol/L, respectively (P<0.05), while the A/P ratio increased significantly from 2.47 to 2.60 (P<0.05). In conclusion, shade significantly increased the NDF, resulting in decreased CP, in vitro digestibility, gas production and VFA concentration. The impacts of shading increased increasing shade level and duration.