The treatment of advanced lower gingival carcinoma requires postoperative chemoradiotherapy; therefore, simultaneous hard-tissue reconstruction may not be indicated. In these cases, mandibular reconstruction is performed using a temporal reconstruction plate and various skin flaps. Herein, we reported 2 cases of advanced lower gingival carcinoma treated with a novel computer-assisted patient-specific, fully custom-made mandibular reconstruction plate system(Cosmofix®)in combination with a pedicle/free flap. In case 1, an 80-year-old female patient was diagnosed with right lower gingival carcinoma( cT4aN3bM0, Stage ⅣB). Under general anesthesia, she underwent tracheostomy, bilateral neck dissection, segmental mandibulectomy, and mandibular reconstruction using Cosmofix® in combination with an ulnar forearm free flap. In case 2, an 81-year-old male patient was diagnosed with right lower gingival carcinoma(cT4aN2bM0, Stage ⅣA). The patient underwent maintenance dialysis and required minimally invasive surgery using a pedicle flap. Under general anesthesia, the patient underwent tracheostomy, right modified radical neck dissection, segmental mandibulectomy, and mandibular reconstruction using Cosmofix® in combination with a pectoralis major myocutaneous flap. Postoperative facial morphology, occlusion, eating, swallowing, articulation, and other dysfunctions were minimal in both the cases. Adjuvant chemoradiotherapy was recommended. In conclusion, the utilization of the Cosmofix® system enabled both esthetic and functional reconstruction following segmental mandibulectomy for advanced lower gingival carcinoma.