Abstract: The objective of this experiment was to investigate the effect of increasing dietary NFC/NDF on populations of B. fibrisolvens,S. bovis and M. elsdenii in the rumen of dairy goats under the condition of induced subacute rumen acidosis （SARA）.Six lactating Guanzhong dairy goats fitted with permanent rumen fistulae were used in a self-contrast experiment design.This experiment consisted of four experimental periods,with ten days in each period.Goats were fed 4 diets with different NFC/NDF （1.02,1.24,1.63 and 2.58,respectively）.The induction of SARA was conducted by gradually increasing dietary NFC/NDF.Realtime PCR was used to detect the populations of B. fibrisolvens,S. bovis and M.elsdenii.The results showed as follows：① The number of B. fibrisolvens and M. elsdenii was both increased with the increasing of dietary NFC/NDF,and when NFC/NDF reached the level of 2.58,the number of M. elsdenii was significantly increased （P0.01）,whereas the number of B. fibrisolvens was significantly decreased （P0.01）.② The number of S. bovis was significantly decreased with the increasing of dietary NFC/NDF （P0.05）,however,during the occurrence of SARA,the number of S. bovis returned to the same level of experimental period Ⅰ.The results indicated that there was no difference in the number of S. bovis at the induced stage of SARA,however,the number of B. fibrisolvens was markedly decreased,whereas the number of M. elsdenii, which is a kind of aciduric bacteria, was significantly increased.