Some glucosidase inhibitors show antitumor metastasis and anti-HIV activities and are also clinically useful for the treatment of diabetes,besides andrographolide derivative have been proven to be potent an α-glucosidase inhibitor.In order to investigate the double effect of glucosidase inhibition activity,a new diterpene lactone derivative 2 was synthesized via reduction of compound 1 which was one of the constitutions of Andrographis Pamicutate(Brum) Nees.The structure of compound 2 was confirmed with X-ray diffraction analysis,NMR,IR,HR-MS and so on.Compound 2 shows a selective α-glucosidase inhibitory activity with inhibition of 49.6% at 100 μmol/L,and the mother 1 has no inhibition activity(100 μmol/L).The results indicate that the double bond can affect the α-glucosidase inhibition activity of andrographolide.