The aim of the study was to evaluate the effects of Saccharomyces cerevisiae fermentation products (SCFP) in calf starter and milk on rumen fermentation and gastrointestinal tract development in the first 56 d of age. Fifteen Holstein bull calves were randomly assigned to one of 3 groups: a texturized calf starter containing 0 (Control), 0.5 or 1% SCFP (Original XPC, Diamond V) of DM from d 4 to 56. In addition, the supplemented calves were fed 1 g/d SCFP (SmartCare, Diamond V) in milk from d 2 to 30. All calves were fed 4 L of colostrum within 1 h of birth and were subsequently fed milk twice daily until weaned at d 56. Rumen fluid was collected by an esophageal tube 4 h after the morning feeding on d 28 and 56 to determine ruminal pH, ammonia N, and volatile fatty acids (VFA). At d 56, all 15 calves were harvested for slaughter weight, and rumen and intestinal morphological parameters. Papilla length (PL) and width (PW) were measured from 5 locations of rumen. Villus height (VH) and width (VW), crypt depth (CD) and villus height to crypt depth ratio (VCR) were measured in duodenum, jejunum and ileum. Data were analyzed by MIXED procedure in SAS with contrast statement to declare Control vs. all SCFP, and 0.5% SCFP vs. 1% SCFP in starter grains. Ruminal pH and ammonia N were not altered by SCFP. However, SCFP supplementation exhibited higher (P < 0.05) ruminal butyrate concentration than Control at d 56. Supplementation of SCFP stimulated (P < 0.05) PL in the rumen. Although SCFP had limited effect on VH, it reduced (P < 0.01) the CD in jejunum, and increased (P < 0.05) VCR in all segments of small intestine, especially when supplemented at a higher dosage in starter. In conclusion, SCFP improved gastrointestinal development, possibly due to increased butyrate production, and greater effect was observed with higher dosage of SCFP.