Our study use continues culture technique through adding mucin as the limiting element in chemically defined culture,medium in order to observe growing states of S.sanguis 34 and,S.mutants Ingbritt(c).The results as follows:S.sanguis 34 were able to grow as pure culture on mucin;S.mutans was unable to grow as a pure culture on mucin,but attained a significant population size in the presence of S.sanguis.These results indicate a synergetic degradation of mucin by S.sanguis and S.mutans in mixed chemism culture.