Protein degradation in the rumen often proceeds at a rate which exceeds the ability of the microbial population to utilize the resulting breakdown products. Bacteria are the most active proteolytic organisms in the rumen, and many species of rumen bacteria are known to be proteolytic (Wallace et al., 1985). The commonly isolated proteolytic bacteria are also able to break down peptides and amino acids, and it was assumed that they were responsible for the ruminal degradation of intact protein through to ammonia. However, studies comparing the specific activities of ammonia production between mixed ruminal bacteria and the well-known proteolytic bacteria noted that no individual bacterium had an activity which could explain the activity of the mixed ruminal culture (Russell et al., 1988). Subsequently, three gram-positive, monensin-sensitive, ammonia hyper producing (HAP) bacteria were isolated from the rumen. The present study reports the sequence of 16sr RNA for ruminal ammoniabacters of Iranian Holstein cows.