Objective: To define key genes relevant to insulin synthesis and exocytosis, and further to investigate the improved process of insulin secretion. Methods: Pancreata of SD rats at embryonic day 12.5(E12.5), E15.5, E18.5 and newborn, 21 days after birth, adult rats were dissected respectively. Genechips from Affymetrix company were applied to explore gene expression profiles. Some genes related to insulin synthesis and secretion were verified by real-time PCR. Intraperitoneal glucose tolerance tests (IPGTT) and ELISA were done to detect the function of pancreatic islet. Islet cells of newborn and adult rats were cultured to observe its shape. Results:Among genes related to insulin synthesis and release, insulin and relevant transcription factors such as PDX-1 began to express from E12.5; Munc13-1, Syntaxin-1a, Rab3a, Vamp-2, Glut-2 began to express from E15.5, while GCK expressed at late stage of embryonic day. Basic blood insulin level was detected at E18.5 and increased rapidly thereafter. However, in response to a glucose load, newborn rats were glucose intolerant,only rats older than a week began to show normal insulin secretory response gradually. The shape of islet cell in newborn rats was similar to adult one, but was much smaller and not so bright. Conclusion:Potential ability of insulin synthesis and release in rat occurs from early and middle stages of pancreatic development. But the normal insulin secretion response to glucose challenge starts later.