This experiment was carried out in order to increase the utilization of feed value of Japanese millet. Japanese millet was seeded on May 9. 1979, and the samples were taken at 7-days intervals for the duration of 45-80 days after seeding. From the feed compositions and in vitro dry-matter digestibility (IVD) measured, the results obtained were as follows; 1. The content of crude protein was highest at 45 days after seeding, and decreased rapidly afterwards. 2. In general, the content of crude fiber increased greatly from 52 to 59 days after seeding, and that of NFE did not change through the period of vegetation. However, the in vitro dry-matter digestibility (IVD) of Japanese millet was high in the early growing stage, and decreased gradually with ageing. The rate of increase of the total digestible dry matter per l0a was highest at the days of 66th and 73th day after seeding. 3. Comparing the content of crude protein with that of crude fiber in the fraction, the content of crude protein in the blade fraction increased as compared with that of crude protein in the sheath-stem fraction in the early growing stage, but that of crude fiber decreased. 4. There was a significant positive correlation (P$lt;0.01) between the in vitro dry-matter digestibility (IVD) of the whole sample by two-stage method and the content of crude protein, and was a significant negative correlation (P$lt;0.01) with the content of crude fiber. There was a significant correlation between the in vitro dry-matter digestibility (IVD) of the fraction and its feed compositions. 5. In the one-stage in vitro dry-matter digestibility (IVD) using rumen liquor procedure of the whole sample, the IVD after 48 hour and 72 hour fermentation was similar each other from 45 to 52 days after seeding, but the variation of the IVD in both fermentation times was found as Japanese millet matured. Comparing the IVD of one-stage method with that of two-stage method, the latter was higher through the period of vegetation.