Primary treatment with brachytherapy for oral cancer is uncommon in large malignant lesions; however, it is preferred by radiation oncologists for initial and smaller-sized lesions in compromised anatomical locations. The purpose of this report is to introduce and discuss the fabrication of a customized brachytherapy applicator for a case of well differentiated squamous cell carcinoma (SCC) of the oral commissures using a radiotherapy thermoplastic mold (RTM). The RTM was molded into the shape of tongs and two acrylic wings were attached to these customized tongs to secure five high-dose radiotherapy catheter tubes. A mouth-stabilizing stent was used to stabilize the oral cavity throughout the brachytherapy process. A total dose of 45.5 Gy was delivered in 13 fractions to the lesion using a Cobalt-60 source over 35 days. At the end of the brachytherapy treatment and a follow-up period of 3 months, the patient responded well, and complete remission of the lesion was observed. The current brachytherapy applicator technique is a simple, viable, and curative option for patients with lesions in difficult -to- access anatomic locations.