Abstract: Spectrophotometer and nitric oxide synthase(NOS) detection kit were used for finding out law of NOS activity in various brain regions of different agegroups rabbits.The results showed: ①NOS activity was detected in every area of rabbit brain, furthermore NOS activity in rabbit cerebellum was higher than diencephalon and brain stem, the lowest activity was found in cerebral cortex②Basically, NOS activity of the young rabbit had developed to the adult rabbit’s level.It developed from maturation to senescence gradually with age.To the aged rabbit, the NOS activity appeared senescence obviously. NOS activity was higher in the adult group than that of young group, juvenile group and the youth group. The lowest NOS activity was found in the aged group. The results indicated that the decreased NOS activity and diminished NO production might weaken role of No on nerve regulation with the rabbit’s doating, which perhaps effect the senescence of rabbit brain, arterial sclerosis and increase in blood pressure.