Rumen development is an important factor determining early solid feed intake and performance in cattle. A popular trend towards early weaning of newborn dairy calves necessitated looking for ways of accelerating the gastrointestinal tract (GIT) development. The present study aimed to determine the effect of sodium butyrate (NaB) supplementation in milk replacer and starter diet on rumen development in rearing calves. Fourteen bull calves (5-day-old) were randomly allocated to two groups: Control (C) and NaB. The later received 0.3 % NaB in milk replacer and starter diet. Animals were in experiment up to age of 26 days. Addition of NaB to milk replacer and starter diet had no effect on daily growth rate, but reduced the weight loss observed in C calves in first 11 days of age. Additionally, the NaB calves weighed more at the end of the study and tended to have higher growth rate in the whole trial period (P<0.15). The NaB calves showed a tendency toward higher reticulorumen weight (P=0.13) and higher reticulorumen weight expressed as a percent of whole stomach weight (P=0.02) as compared to control. Histometry analysis indicated larger rumen papillae length and width (P<0.01) in NaB group, and no change in muscle layer thickness, as compared to control. Plasma glucagon-like peptide-2 relative increase was higher in NaB group than in C group, and may be involved in rumen development. In conclusion, supplementation of the diet (milk replacer and starter diet) with NaB may enhance rumen development in neonatal calves.