Abstract: Rice grain filling is a process of starch accumulation. Biosynthesis of starch from sucrose in the developing endosperm primarily determines grain yield and quality of rice. DNA microarray analysis was performed in this study to investigate the differential expressed genes between 3 days and 9 days post anthesis in rice spikelets. 59 starch biosynthesis related genes were screened and among these, 20 genes were 2-folds up-regulated at 9 days post anthesis (DPA) compared with 3 DPA, including SUS2, AGPS2, AGPL2, GBSS Ⅰ, SS Ⅱ a, BE Ⅰ, which could be the key genes responsible for the starch biosynthesis during grain filling. 12 genes were down-regulated at 9 DPA compared with 3 DPA, including CIN2, SPS3, AGPL1, GBSS Ⅱ, SS Ⅲ b, which were presumed to be involved in the construction of fundamental cell machinery and initation of starch granules.