Effects of increasing dietary rice straw on chewing activity, ruminal fermentation, and fibrolytic enzyme activity in growing goats were investigated in a 4×4 Latin Square experiment. The goats were offered four diets with an increasing proportion of rice straw (i.e. 0.05, 0.10, 0.15 and 0.20, respectively, on dry matter basis). Increasing level of rice straw increased (P linear effect <0.05) the time spent on eating, ruminating, and chewing. The ruminal pH and acetate: propionate ratio were increased (P linear effect <0.05), while the NH 3 -N concentration was decreased (P linear effect <0.01). Increasing level of rice straw in the diet increased (P linear effect ≤0.01) molar proportion of acetate and isovalerate, and decreased (P linear effect <0.01) molar proportion of propionate. The CMCase, xylanase and cellobiase activities in the rumen were decreased (P linear effect <0.05) with increasing level of dietary rice straw, whereas the avicelase activity was increased (P linear effect <0.01). In summary, increased level of rice straw elevated the dietary neutral detergent fibre (NDF) content in the diet and had a great impact on chewing activity and ruminal fermentation.