Two groups of gilts were fed from 10 to 25 kg BW on a standard low fibre (LF) diet, and two groups on a LF diet supplemented with 10 or 20% grass meal ( MF and HF diet, respectively). The fibre content was 37.9, 53.5 and 76.4 g/kg in the LF, MF and HF diets, respectively. At 25 kg BW the pigs from one group fed on LF, and groups on MF and HF diets, were assigned to the LF diet, while a second group fed on LF was transferred to the HF diet. After 14 days the pigs were slaughtered and samples of mucosa from the proximal, middle and distal part of the small intestine were taken and analysed for the activity of sucrase, aminopeptidase A and N, and dipepidyl peptidase IV. The activity of peptidases was higher in pigs fed MF and HF diets from 10 to 25 kg and the HF diet 14 days before slaughter than in animals continuously fed on the standard LF diet, while the activity of sucrase was higher in pigs fed on the MF diet from 10 to 25 kg than continuously on the LF diet.