In order to investigate the effect of orally supplemented urea on utilization of low-quality roughage in sheep, digestion and nitrogen balance trials were conducted using 3 Japanese Corriedale rams fed a mixed hay supplemented with urea at 3 levels, i. e., 0, 15 and 30% of dietary nitrogen from hay, according to a 3X3 Latin square design. The results obtained were as follows; 1) The digestibility of crude protein was clearly (P<0.05) increased with an increase of urea supplemented orally. 2) Urinary nitrogen excretion was fairly increased with an increase of oral urea supplement, and thus, the retained nitrogen increased a little after supplementing urea at a level of 30% dietary nitrogen. 3) Ruminal ammonia level clearly (P<0.05) increased with an increase of oral urea supplement. On the contrary, the level of ruminal VFAs tended to be lower after feeding hay with urea than after feeding hay alone. 4) The concentration of blood urea-nitrogen tended to increase with increase in supplemented urea, and the plasma total protein did not change with an oral urea supplement.