A twelve-year-old, female Hermann’s tortoise (Testudo hermanni) was presented with an oviductal prolapse after showing tenesmus for three days prior to presentation. Radiography revealed a soft tissue opacity in the caudal coelomic cavity that ultrasonographically presented as a congested, invaginated tubular structure and was deemed to comprise the left oviduct. After repositioning the oviductal prolapse, coelioscopy confirmed that the invaginated structure consisted of the anterior part of the left oviduct and incorporated a part of the ipsilateral mesovarium and mesosalpinx. A transplastron osteotomy was carried out to perform unilateral salpingectomy and bilateral ovariectomy. A definitive diagnosis of an oviductal leiomyoma was made based on histopathological and immunohistochemical examination of the invaginated part of the oviduct. In the present case, the authors highlight that neoplastic disorders should be considered as a cause of oviductal invagination and prolapse in chelonians. To the authors’ knowledge, this is the first report of the diagnosis and successful treatment of an oviductal leiomyoma in a Hermann’s tortoise.