Background: Anosmia has been considered as the first diagnostic criteria of Parkinson disease (PD), we investigated the effect of the olfactory bulbectomy (OBX) on histopathological features of the substantia nigra in an animal model. Methods: Twenty-seven male rats were used in this study. Animals were divided into three groups as five (control), six SHAM and sixteen study (OBL) groups. Nothing was done in the control group, the only burr hole was done in the SHAM group, OBL was not applied, and bilateral OBL was performed in the study group, and followed ten weeks, then animals were decapitated. Olfactory bulb volumes were measured by macro anatomically. The olfactory bulbs and substantia nigra sections were analyzed by a stereological method to evaluate olfactory glomerulus and neuron density of substantia nigra per cubic centimeter and compared with statistically. Results: The mean olfactory bulb volume, degenerated olfactory glomerulus density and degenerated neuron density of substantia nigra were measured as:(4.14 +/- 0.20) mm(3), (1 +/- 1)/mm(3) and (7 +/- 2)/mm(3) in control (Group I); (3.6 +/- 0.16)/mm(3), (4 +/- 1)/mm(3) and(32 +/- 7)/mm(3) in SHAM (Group II) and (2.2 +/- 0.9)/mm(3), (112 +/- 18)/mm(3) and (1543 +/- 115)/mm(3)in study group (Group III). Diminished olfactory bulb volume was observed in Group III animals. Conclusions: We concluded that OBL may lead to the degeneration of substantia nigra.