Abstract: This study investigated the effects of dietary nitrate dosage on ruminal nitrate disappearance rate, fermentation parameters and blood methemoglobin of Hu sheep. The experiment used a randomized block design. Six selected Hu sheep were fed different levels of dietary potassium nitrate (0%, 1%, 2%, 3%, 4%, 5% of DM intake). The concentration of nitrate, nitrite and fermentation parameters in rumen fluid were obtained 0, 0.5, 1.0, 1.5, 2.0, 4.0, 6.0 and 8.0 h after feeding. In addition, the concentration of blood methemoglobin was determined 2.0 h after feeding through blood collection from the jugular vein. The nitrate concentration increased to a maximum value (0.95-2.14 g/L) at 1.0 h after feeding, then reduced rapidly. The nitrite concentration increased to maximum value (0.93-6.22 μmol/L) 1.5 h after feeding. The content of methemoglobin significantly increased with the nitrate addition (P<0.01), to a peak of 0.32% at 5% dietary potassium nitrate. Nitrate addition also significantly increased rumen fluid pH value, ammonia nitrogen concentration and acetic acid/propionic acid 2.0 h after feeding (P<0.01). In conclusion, potassium nitrate addition at over 3% of DM intake was found to reduce the concentration of microbial protein and total volatile fatty acids. Microbial protein synthesis and total volatile fatty acids were highest with 2% potassium nitrate addition, and the dosage of 2% potassium nitrate was beneficial to rumen fermentation.