Objective: To observe the change in nitric and nitric oxide synthase in limbic system in the rat brain under slow stress. Methods: The slow stress condition was induced by restricted movement of rats, during which the level of NO and activity of NOS were measured in hippocampus, prefrontal and hypothalamus. Results: The level of NO and activity of NOS of hippocampus, hypothalamus and prefrontal in stress group was significantly higher than that in the control group ( P <0.05). Conclusion: The level of NO increased in brain tissues might play a role in stress related disorder.