Aim: The aim of the study is to investigate the effect of prenatal treatment of metronidazole on the process of cerebellar foliation in the guinea pig. Introduction: The use of metronidazole in pregnancy still occupies very different attitudes among doctors who prescribe them. Neurotoxicity is a common side effect in the use of metronidazole, but there is still no clear animal study. Materials and Method: We studied 42 guinea pig fetuses obtain from 12 pregnant guinea pig dams.  Dams were separated in experimental (6) and control6) group(K). Experimental group(E) received from 42-49 day of gestation at every PLENARY ORAL PRESENTATION 22 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. 12 hour (at 8 a.m. and 8 p.m.) subcutaneous injection od saline solution of metronidazole in concentration of 28 mg/kg.  Control group received using same time protocol just saline solution. At 50th day of gestation all dams were sacrified and fetuses were used for further analysis. In each  fetuses (22 in E, and 20 K group). Firstly we make gross picture of the brain and secondary we separated vermis region for further histological and immunohistochemical analysis. Results: An analysis of macroscopic images of the dorsal side of the cerebellum in the experimental group of individuals revealed malformations in 15 out of 22 fetuses (68.2%). The most affected folia was VII and characterized with aberrant diagonal positioning along the entire dorsal side of the vermis. Other folia were partial presence, with micro, and agyria changes. Conclusion: Prenatal use of metronidazole in guinea pigs during the 42-49th day of gestation cause disturbance in cerebellar foliation.