A simple method for the comparison of bacterial populations from a large number of samples using the host-specific bacteriophage was described. Xanthomouas oryzae No. 60 and its specific phage were used for this purpose. Samples of bacteria are suspended in Ca Vf Ch medium or potato semi-synthetic medium, and added with phage suspensions to make the final concentration of 10^3-5 per ml. The samples were then incubated under optimum temperatures and under shaking at 80 rpm to propagate the added phage. Three hours later, aliquots were pipetted out from the centrifuged (6000 rpm, 5min.) supernatant and plated with the indicator strain of bacteria, to make plaque countings. It was confirmed that the number of plaques are usually proportional to the number of bacteia initially contained in the sample. This method will be favorably applied for studies on plant resistance against bacterial diseases, effects of bacteriocides, and other subjects, where problems may be dissolved on the basis of bacterial number contained in the plant tissues.