The effect of thermal energy due to drilling around the facial nerve canal on the facial nerve was histopathologically evaluated in four guinea pigs. The bony canal of the facial nerve was drilled using a 3mm diamond burr for one minute. The temperature changes on the facial nerve canalwere noted before and after dissection. The temporal bones of the animals were histopathologically examined under light microscopy using haematoxylin & eosin (H&E) and solochrome cyanine staining for myelin, and immunohistochemical staining for neuronal nitric oxide synthase (nNOS). Compared to the control group, it was observed with H&E staining that there was oedema among the axonal fibres and with solochrome cyanine staining that the thickness of the myelin fibres was decreased, and that the severity and extent of nNOS activity was decreased in the axonal fibres. It was concluded that a temperature increase on the facial canal may potentially lead to inflammation of the nerve, and may also cause deterioration of nerve conduction to some extent.