The pancreas is an important organ, which contains two distinct populations of cells, the exocrine cells that secrete enzymes into the digestive tract, and the endocrine cells that secrete hormones into the bloodstream. We studied the pancreas of rats which divided into two groups referred to 20-days-old rat fetuses and three-days-old newborns via both with quantitative and microscopical methods. At the end of the study; pancreas samples were obtained from all animals. Stereological estimations were performed on total pancreas volume, Langerhans islet’s volume and islet cell number. The histological structure of pancreases of these two groups was also evaluated at light and electron microscopical levels. According to our results; morphological differences between fetuses and newborns, were statistically significant. These results indicate that rat’s pancreas development continues after the birth. Further studies needed to determine of that question which period of life pancreas development is complete.