Abstract: The change of α_amylase activity and isoenzyme in embryos of Nongk en 58F, Nongken 58S and Nongken 58 were analyzed by assay of reducing sugars with 3,5_dinitrosalicylic acid(DNS) and acrylamide gel electrophoresis technique under the different germinating time. The α_amylase activity in the embryos of both Nongken 58F and Nongken 58S were higher than that of Nongken 58 from 0 to 36 h germinating time. Rice seed embryos had 5 isoenzyme bands(A1,A2,A3,A4,A5). A2,A4 and A5 were present in the embryos of Nongken 58F, Nongken 58S and Nongke n 58. A3 was specific for both Nongken 58F and Nongken 58S. A1 was specific for the embryos of Nongken 58. These results suggested a higher α_amylase activity be necessary for promoting fast germination of rice seeds, α-amylase isoenzyme A1 and A3 may play an important role in regulation of germination speed.