Introduction: Recent data shows that retinoic acid (RA) signaling is required for early pancreatic development in animals, whereas the effects of exogenous All-trans Retinoic Acid (ATRA) on gestation day (GD) 10 in later development have not been well documented. Materials and Methods: In this experimental interventional study, female rats, were randomly divided into two groups (experimental and control, n=5 each). Animals in the experimental group received single dose (100 mg /kg) of ATRA orally on GD 10 and fetuses were observed on GD 18.The fetus pancreas (from both the experimental and control groups each n=24) were processed for staining and followed by measuring the accumulation of pancreatic acinus and pancreatic ductile associated with the islets of langerhans. In addition, the mean diameter of pancreatic acinus, acinar cells and related nucleus were measured. Statistical analysis was done by student t-test, P value<0.05 being considered significant. Results: In the experimental embryos on GD 18, the mean accumulation of pancreatic acinus (23.5%), and pancreatic ductile, associated with the islets of langerhans (76%) per field were increased. There was a significant difference in accumulation of pancreatic acinus (P< 0.0001) and pancreatic ductile, associated with the islets of langerhans (P< 0.0001), between the groups in this regard. The mean diameter of pancreatic acinus and the related nucleus were compared in the two groups, and results showed significant (P< 0.0001) decrease of this parameter in the experimental group. Conclusion: Results suggest that ATRA may have positive effects on proliferation, differentiation and maturation of pancreatic acinus and pancreatic ductile associated with the islets of langerhans.