Spindle cell squamous cell carcinoma is a rare tumor in the oral cavity with an appearance similar to sarcoma, and is classified as a subtype of squamous cell carcinoma. In this study, we report a case of spindle cell squamous cell carcinoma simultaneously occurring in the buccal mucosa and mandibular anterior gingiva after chemoradiotherapy for squamous cell carcinoma. <br>The patient was a 68-year-old woman who came to our hospital in September 2009 with a complaint of a white lesion on the right buccal mucosa and mandibular anterior gingiva. We diagnosed it as squamous cell carcinoma and performed preoperative concurrent chemoradiotherapy and tumor resection. Local recurrence and new occurrence of squamous cell carcinoma were observed in the right buccal mucosa in May 2011, right lower lip in January 2012, right floor of the mouth in December 2012, right buccal mucosa in June 2013, and mandibular anterior gingiva in November 2013. Therefore, we performed resection and preoperative chemotherapy or concurrent chemoradiotherapy, respectively. In February 2014, masses were found in the right buccal mucosa and mandibular anterior gingiva, and the pathological diagnosis of biopsy was spindle cell squamous cell carcinoma. Therefore, we performed resection. In April of the same year, a leukoplakia was found on the left side of the floor of the mouth. We performed resection, and the pathological diagnosis was squamous cell carcinoma. In June of the same year, recurrence of the tumor was observed in the right buccal mucosa, but the patient did not wish to have surgery and died in August of the same year.