We observed that oil began to accumulate at 25 seed days after flowering (DAF) and reached the maximum potential at 35 seed DAF of oilseed rape, and the greatest weight of 100 seeds was obtained at 35 seed DAF. To survey a broad analysis of gene expression in developing embryos of Brassica napus, the Bn 300k microarray have been constructed. The Bn 300k Microarrary was designed from 80,696 unigenes clustered from 543,448 ESTs and 780 cDNA at NCBI. These arrays have been hybridized in a series of experiments with probes derived from seeds and leaf of B. napus. Approximately 8.5% of the 7,000 genes were expressed as ratios 2-fold higher in seed (25 DAF) than leaves and 0.4% at ratios 10. Also we observed that storage and cell differentiation-related genes were highly expressed at 10 DAF, whereas energy-related genes including fatty acid metabolism were increased up depending on seed maturation using Microarray, which was confirmed by reverse transcriptase polymerase chain reaction. These results suggest that B. napus arrays provide a very useful data set of seed-specific expression that can be further analyzed by examination of the promoter regions of these genes and help our understanding of the complex regulatory network in developing seeds.