Objective: To define gene expression profiles during late stage of embryonic pancreatic development of rats and to find out key genes in rat pancreatic functional development. Methods: Pancreata of rats in embryonic day 15.5(E15.5) and 18.5(E18.5)were dissected under microscope respectively. Genechips from Affymetrix company were applied to study gene expression profiles. Some differentially expressed genes were verified by RT-PCR. Results: Comparing El8.5 to El5.5, 8.3％ genes were expressed differently 2-fold above, in which, 50.3％ were up-regulated, including transcriptions related to metabolic development and various kinds of enzymes and hormones (both endocrine and exocrine) and 49.7％ were down-regulated, including transcriptions related to cell differentiation. The percentage of genes having definite function was 63％, and that of expressed sequence tag(EST) was 37％. The result of RT-PCR is accordant to that of genechips. Conclusion: The metabolic function of rat pancreas may be further accomplished during late stage of embryonic day.