Background: Nitric oxide (NO) is produced in different body organs in mammals and numerous physiological and pathological properties are attributed to this small molecule. The precursor of this substance in the body, L-arginine, is synthesized by the enzyme nitric oxide synthase (NOS), and it is catalyzed, and is inhibited by a substance called L-NG-nitroarginine methyl ester (L-NAME). In this study we investigated the qualitative and quantitative effects of nitric oxide on cerebellar histopathology in vivo environment via increasing and decreasing its production.Methods: Forty Wister rats, weighing 200- 250 gr with a mean age of 8 weeks, were divided into 5 groups after making sure the rats were pregnant. Except the control group, the other pregnant groups, respectively received: 2 ml/kg normal saline, 200 mg/kg L-arginine, 20 mg/kg L-NAME and a mixture of the same doses of L-arginine and L-NAME on the third, fourth and fifth days of pregnancy. On day 18 of pregnancy, we anesthetized the rats, excised the cerebellum after craniotomy and fixed the organs in 10% formalin. We later prepared 5 to 6-micron in thickness tissue sections and dyed them by the routine Hematoxylin and eosin (HE) and Masson's Trichrom staining methods before studying them by light microscopy.Results: There was a significant difference between the rats receiving L-arginine and the rats in other groups (P<0.01). Conclusion: This study showed that L-NAME is capable of significantly decreasing the injury caused by nitric oxides in rat cerebellum.