Abstract: Sugar beet pulp and alfalfa hay meal were selected as main fiber sources in tested diets to study on the effects of three levels of dietary fiber on nutrient digestibility, development of digestive tract and activity of digestive enzyme in growing pigs. 60 pigs (Duroc×Landrace×Yorkshire) were divided into three groups. Three levels of fiber were 3%, 6% and 8%. The results showed: (1) The digestibility of gross energy, dry matter, crude protein and neutral detergent fiber decreased significantly with increasing fiber level (p<0.05); (2) The level of crude fiber was 8%, significant trophic effect on the pancreas and colon were found (p<0.05); (3) The activity of proteolytic enzyme, trypsin, chymotrypsin increased (p<0.05) in the pancreas.