It is known that high molecular weight components of gelatin (Fraction H) are degraded by irradiation of ultrasound. We have been studying this process minutely with a rather high concentration solution of gelatin. In this study, we irradiated a low concentration (less than 1.00 wt%) gelatin solution with ultrasound in order to study the effect of dilution. The degradation process of fraction H was also found to be of the first order and dilution had no special effect on the degradation process. In the process of the experiment, we found out the contents of fraction H determined by HPLC differed with the concentration of the sample gelatin in the case of less than 1%. There was a possibility that fraction H was degraded by dilution and it was reconstituted by reconcentration of the diluted solution.