Brachytherapy is often applied to oral cancers, with good outcomes and minimal loss of oral function. Especially, mold brachytherapy is best suited for superficial oral cancers with little or no bone invasion, such as gingival cancer, palatal mucosal cancer, or buccal mucosal cancer because of the thin tissue thickness that needs to be irradiated. A few cases have been reported on mold brachytherapy for gingival cancers, especially with high-dose-rates (HDR), these treatments were performed during hospitalization. We report a case of lower gingival squamous cell carcinoma (SCC) treated with HDR mold brachytherapy in an outpatient setting. A 71-year-old male with lower gingival SCC had received HDR mold brachytherapy (54 Gy, 9 fractions, 5 days) as an outpatient. Eighteen months after the mold therapy, the patient had no recurrence and no metastasis. A search of the literature revealed no previous report of a case of gingival cancer treated with HDR mold brachytherapy in an outpatient.