The aim of this study was to determine the effect of different dryer outflow temperatures (123 vs. 153°C) imposed during dehydration of grass, on the digestibility of rumen undegraded dietary protein (UDP) in rats. UDP was the residue obtained after incubation of dehydrated grasses (DG123 and DG153) in the rumen of sheep for 12 hours. The protein in the diets for rats was derived from egg white (70%) and UDP (30%). Compared to DG123, DG153 had a higher proportion of ADIN in total N (10.46 vs. 23.91%) as well as significantly higher ruminal degradability (39.8 vs. 34.6; P < 0.01). In the trial with rats, both apparent and true digestibility of UDP from DG153 (88.0 and 92.6%) were significantly higher than from DG123 (85.7 and 90.5%). This may suggest that a temperature of 153°C can protect protein against degradation in the rumen without any unfavourable effect on intestinal digestibility.