A palatal augmentation prosthesis (PAP) is used to facilitate improvement in the speech and swallowing functions of patients with tongue resection or tongue movement disorders. However, a PAP's effect is limited in cases where articulation disorder is severe due to wide glossectomy and/or segmental mandibulectomy. In this paper, we describe speech outcomes of a patient with an articulation disorder following glossectomy and segmental mandibulectomy. We used a palatal plate (PP) based on a PAP, along with an artificial tongue (KAT). Speech improvement was evaluated by a standardized speech intelligibility test consisting of 100 syllables. The speech intelligibility score was significantly higher when the patient wore both the PP and KAT than when he wore neither (p＝0.013). The conversational intelligibility score was significantly improved with the PP and KAT than without PP and KAT (p＝0.024). These results suggest that speech function can be improved in patients with hard tissue defects with segmental mandibulectomy using both a PP and a KAT. The nature of the design of the PP and that of the KAT will allow these prostheses to address a wide range of tissue defects.