Experiment was carried out to measure digestibility and voluntary intake in horses and digestible nutrients of timothy hays harvested at different times in Hidaka district of Hokkaido. First cutting hays harvested on different swards from Tune 8 to July 28 were used. In horses, the dry matter digestibility of hay decreased as the harvest time was delayed; the digestibility of hay harvested on June 8 was 57%, whereas that harvested during late July was about 30%. Similarly, digestibility of crude protein, acid detergent fiber and energy of hays decreased with maturity advancement. Significant relationships were found between the digestibilities in dry matter, in energy and the growing period. As the harvest time was delayed these digestibilities decreased to 0.5% unit per day. Digestible energy of hays also decreased considerably, ranging from 2.52 to 1.41 kcal/g, with advancing maturity. There was no relation ship between the dry matter intake and dry matter digestibility of hays. In sheep, digestibilities of dry matter and nutrients and digestible energy of hays decreased with maturity advancement as well . However, the rate of decrease in digestibility with maturity advancement was less than that of digestibilities in horses .