Male weanling Sprague Dawley rats were used to evaluate the effect of dietary rice starch with different particle size on growth performance, intestinal function and proliferation. There were two dietary treatment: rice starch (RS), ultra finely pulverized rice starch with less than $15{mu}m$ size (PRS). They were eight rats per treatment. In vitro digestibility, body weight change and organs weight were evaluated. Serum GPT, GOT and blood urea nitrogen were analyzed. Transit time, short chain fatty acid contents of cecum, and cell proliferation of duodenum and jejunum were measured. In vitro digestibility of PRS was higher than that of RS. Rats fed ultra finely pulverized rice starch for 3 weeks grew faster than rats fed rice starch. PRS group has higher weights of liver, kidney, spleen and epididymal fat pad, perhaps as a result of increased digestibility. GPT and GOT were not different between two groups. Blood urea nitrogen was higher in RS-fed rats than that of PRS-fed rats. Feeding ultra finely pulverized rice starch resulted in a proliferation of duodenum significantly. These results suggest that ultra finely pulverized rice starch increases the growth performance in weanling animals with reduced number of cells in the cell cycle of small intestine.