Using real-time PCR method to detect the effects of varying levels of triticale dried distillers grains with solubles (TDDGS) inclusion in beef cattle diets on the populations of three rumen Prevotella species viz., Prevotella ruminicola, Prevotella brevis and Prevotella bryantii. The results showed that 1) compared with control group (CG), the populations of P. ruminicola and P. brevis in all TDDGS groups (20%, 25% and 30% TDDGS) increased, and a 47-fold (P < 0.05) and a 794-fold (P < 0.05) significant increase were observed in 20% TDDGS group respectively, however, the population of P. bryantii decreased in all TDDGS groups and a 5-fold (P < 0.05) significant decrease was found in 20% TDDGS group; 2) compared among TDDGS groups, significant population difference was only observed between 20% and 30% TDDGS groups for P. ruminicola, however, no other significant population differences were found between the TDDGS groups for the three Prevotella species. The conclusion was that incorporation of 20% TDDGS in beef cattle diet significantly affected the populations of all three rumen Prevotella species but no obvious population changes were found between the TDDGS groups.