Freeze-dried flowers of the Akinowasuregusa (Hemerocallis fulva L. var. sempervirona M. Hotta), a Hemerocallis genus of the lily family, were fed to C57BL strain mice. The slow wave sleep and paradoxical sleep of the Hemerocallis-treated group increased during the dark period. The differences between the control group and the Hemerocallis-treated group were significant (P < 0.05). The Hemerocallis feeding did not cause a change in sleep time during the light period. As a result, there was no significant change in the sleep-time percentage over a 24-h period.