This study was conducted to study the effects of N-acetyl-DL-methionine (NAM) on environmental parameters in rumen and the apparent disappearance rate in forestomach of sheep. Four 35 kg Boer goat wethers fitted with ruminal and duodenal cannulas were used in a 4×4 Latin square design, and were ruminally administered with graded levels of NAM (0, 4, 6 and 8 g/d, respectively); the experiment consisted of 4 periods with 16 days per period (10-day pre-experiment and 6-day experiment). The samples of rumen fluid and duodenal chymus were collected in the first 3 days and the last 3 days of experimental period, respectively, to determine evacuation rate, pH and osmotic pressure of rumen fluid, and the apparent disappearance rate of NAM. The results showed as follows: 1) the evacuation rate and pH of rumen fluid of sheep administered with 6 and 8 g/d NAM were significantly decreased (P<0.05), however, the osmotic pressure of rumen fluid was significantly increased (P<0.05). 2) The mean of apparent disappearance rate of NAM in forestomach after administered for 1.5 to 12.0 hours was 68.0% to 74.9%, and the disappearance rate of NAM in rumen after administered for 12.0 hours was 79.8% to 86.9%. In conclusion, NAM is not beneficial for ruminal digestion environment, it can decrease evacuation rate and pH, but increase osmotic pressure of rumen fluid, meanwhile, it has high apparent disappearance rate in forestomach (about 80% after 12 hours). Under condition in the present study, the ruminal administration of 6 and 8 g/d NAM has greater adverse impacts on sheep.