The ruminal bacteria eluted from the rumen digesta solids, obtained from the rumen contents of sheep, 4 hr. after the administration of feed, were fractionated into 3 portions. The digesta solids were subjected to an elution treatment, 1st with simple salts solution and subsequently with the salts solution containing Tween 80. With this treatment, the 1st washing fraction (W1 fraction), 2nd washing fraction (W2 fraction), and Tween fraction (T fraction) were obtained, respectively. Each fraction, including the guaze filtrate fraction, was studied for the distribution in those fractions of cell numbers for 7 groups of cell types, and for 9 representative strains isolated from the rumen contents. Chemical composition of the rumen digesta solids was investigated. The solids were enriched with crude fiber as compared with the supplied ration. There were only slight differences in the composition of the solids between both the rumen contents of animal, 4 hr. and 24 hr. after the administration of feed. G fraction was higher in number of cells compared to other fractions, and over 1/2 of the total rumen bacteria was distributed in this fraction. While, T fraction exceeded W fraction in cell number and contained ca. 23-28% of the total rumen bacteria. The morphological features of the bacterial cells in each fraction were examined by means of the electron microscope. The group of small cocci was most abundantly distributed in each fraction and amounted to 58-65% of total bacterial cells. Both .groups of long and short rods followed the above group though in much smaller number. T fraction contained an appreciably higher number of long rods than other fractions. The distribution in each fraction of 9 representative strains of the rumen bacteria was investigated by employing the fluorescent antisera method. It was observed that the distribution of the bacteria in the rumen contents was accomplished due to their physiological characters. The results obtained were assessed from the ecological point of view.