Abstract: The effects of cysteamine （Cs） on pH, total dehydrogenase and TVFA in the rumen of weaned lambs of Tibetan Sheep were studied. 10 80-day-old weaned lambs of Tibetan Sheep with loading permanent rumen fistula and the average initial weight of（16.00＆#177;0.31）kg were randomly divided into two groups（test group and control group）. 300 mg/（kg＆#183;BW） of Cs was added in the diet concentrate every two days. The test period lasted for 42 days. 10 mL vein blood samples and tumor gastric juice were collected at 7：00, 9：00, 11：00, 13：00, 15：00, 17：00, 19：00, 21：00, 23：00, 1：00, 3：00 and 5：00 on the 0th, 7th, 14th, 21st, 28th and 35th days. And pH, total dehydrogenase activity and TVFA in the rumen were determined. The results showed that adding Cs in the concentrate in the test group increased pH of rumen juice in the weaned lambs of Tibetan Sheep and decreased the concentration of urea nitrogen in the serum, which had significant difference with control group （P〈0.01）. And the activity of total dehydrogenase in gastric juice was significantly enhanced （P〈0.01）. In the whole test period, Cs had extremely significant influences on TVFA in the rumen.