Aim To investigate aminoguanidine （AG） inhibitory effect on semicarbazide-sensitive amine oxidase （SSAO） in vitro and in viva,and the prevention of vascular complications in diabetic rats.Methods SSAO enzyme from aorta homogenates of male SD rats,benzylamine was used as artificial substate for the catalytic reaction of SSAO.A series concentration of AG were added in the enzymatic reaction system,using high performance liquid chromatography to detect SSAO enzyme activity.35 male SD rats were randomly divided into normal control （NC） group,diabetic model （DM） group and DM＋AG group,using a single intraperitoneal injection of streptozotocin （STZ） induced diabetic model,AG （25 mg/kg） was administered daily via intraperitoneal injection in DM＋AG group.Plasma SSAO enzyme activity,methylamine,formaldehyde,endothelin-1 （ET-1）,nitric oxide （NO） were detected after 8 weeks later,while aortic tissue SSAO enzyme activity was detected.Morphology of aorta and kidney in all groups were observed under light microscope and transmission electron microscope.Results AG was strongly inhibited rat aortic tissue SSAO enzyme activity,IC₅₀ was 12.47 μmol/L.SSAO enzyme activity,ET-1 concentration in DM group were higher than those in NC group while plasma NO concentration was decreased （P<0.01）.AG can strongly inhibit SSAO enzyme activity in diabetic rats,reduce ET-1 level,elevate methylamine,NO concentration （P<0.01）.The pathological changes of aorta and kidney in DM＋AG group were less serious than DM group.Conclusion AG can effectively inhibit SSAO enzyme activity.The preventive effect of AG on diabetic vascular complications may inhibit SSAO oxidative deamination effect.