One of the reasons of weight loss and poor performance in horses is decrease in food intake. Oral cavity problems can cause malfunctions in prehension and deglutition resulting in dysphagia. There are few published reports about a metallic foreign body disorders in the oral cavity of horses due to an important role of their flexible lip and incisor teeth in food selection and prehension. This report describes the history, clinical, hematological and radiographic findings and surgical management of a left oral wall fistula formation due to a piece of wire penetration in a pregnant mare. The wire was removed through surgical intervention in a standing position of the horse under mild sedation and local anesthesia. One-month follow-up examination showed that the mare had regained her previous work performance with no post-operative complication. Precise oral examination and using an ancillary diagnostic device such as radiography can be suggested for oral cavity pathologies detection and accurate diagnosis in horses.