Penetration of different kinds of peptides or collagen peptide through the intestinal membrane was studied in two experiments using anin vitrorat everted intestine penetration model. In Study 1, twelve 11-wk-old rats (Wistar strain) were randomly divided into two groups and penetration of whey peptide (n=6) and soy peptide (n=6) through the intestinal membrane was compared. In Study 2, fourteen 11-wk-old rats (Wistar strain) were divided into a control group (n=7) and a training group (treadmill running at a speed of 20-35 m/min for 15 mm day, 5 days wk for 4 wk n=7), and penetration of collagen peptide through the intestinal membrane was investigated in the two groups. In Study 1, the quantity of whey peptide that penetrated through the intestinal membrane was significantly greater than that of soy peptide (P<0.01) . In Study 2, body weight was significantly lower in the training group than in the control group except during 12 and 12.5 wk of age (13.5 wk ; P<0.01, others; P<0.05) . The weights of heart, kidney, and spleen were significantly increased, and the weight of fat was significantly decreased in the training group compared to the control group (P<0.05, P<0.05, P<0.01, P<0.05, respectively) . In both groups, a portion of collagen peptide penetrated through the intestinal membrane; but there was no significant difference in quantity between the two groups. In conclusion, the inhibition of weight gain in the training group was possibly caused by decreased feeding from lack of appetite with enforced exercise. These findings suggest that whey peptide penetrated through the intestinal membrane in greater quantities than soy peptide, and collagen peptide is not affected by enforced exercise.