Effect of reducing dietary rice straw on N balance, site and extent of digestion, and efficiency of microbial protein synthesis were evaluated in this trial. Four Liuyang black goats (average body weight 19.3±2.1 kg), fitted with the ruminal, proximal duodenal and terminal ileal cannulas were used in a 4×4 Latin square design. Goats were assigned to four dietary treatments designed by increasing maize grain inclusion at the expense of rice straw: 1. 40% forage (20% maize stover and 20% rice straw, HR); 2. 35% forage (20% maize stover and 15% rice straw, MR1); 3. 30% forage (20% maize stover and 10% rice straw, MR2) and 4. 25% forage (20% maize stover and 5% rice straw, LR). Experimental diets were similar in chemical composition except for dietary NDF and metabolizable energy content. The amount of diet offered to each goat was restricted to 85% of its ad libitum intake to maintain no orts during the whole experimental period. There were no differences in DMI as a result of restricting intake. Totaltract digestibility of OM (P<0.01), N (P<0.01) and NDF (P<0.05) increased with reducing dietary rice straw. Retained N increased from 12.04% for HR to 21.62% for LR (P<0.01). Efficiency of microbial protein synthesis was not affected by dietary rice straw (P>0.05). When expressed as a percentage of N intake, ruminal N disappearance was not affected (P>0.05) by treatments. The true ruminal OM, apparent ruminal OM and ruminal NDF disappearance increased (P<0.01) with reducing dietary rice straw. There were no differences (P>0.05) in small intestinal digestibility of OM and N among the treatments.