In the present study, effect of the changes in daily light（L）and darkness（D）cycle on rumination behaviour in sheep fed roughage alone at a level of２．０or ２．２％ dry matter per bodyweight per day in２times feeding a day or hourly feeding. The ４daily lighting treatments were as follows; Treatment I,１２L＋１２D; Treatment II,６L＋６D ＋６L＋６D; Treatment III,２４L, and Treatment IV,２４D in trial１, and in trial２, Treatment I,１２D＋１２L; Treatment II,６D＋６L＋６D＋６L; Treatment III,２４D and Treatment IV,２４L. During the sampling period in each lighting treatment, the time spent chewing during eating and ruminating was recorded. The eating behaviour was observed in each hour during lighting period in２times feeding a day. Daily eating pattern after hourly feeding was relatively steady in all the４lighting treatments. Daily total time spent ruminating tended to increase in Treatments I and II in２times feeding a day, and in hourly feeding the tendency was in opposition. There was no rumination at１hour after morning and evening feeding in２times feeding a day. In hourly feeding, on the contrary, there was no zero time spent ruminating per hour in all the lighting treatments. During continuous lighting, the rumination pattern in the first half（０９：００−２１：００）and the latter half（２１：００−０９：００）was very similar after２times feeding a day, and that after hourly feeding was relatively steady for２４hours. From these findings, it was confirmed in ruminant animals that the changes in daily lighting condition, in particular daily darkness pattern, could have clearly influenced on initiation of rumination behaviour.