Osseous metaplasia is an extremely rare occurrence in traditional serrated adenoma (TSA). We report a case of a 50-year-old female with a TSA with osseous metaplasia (OM). The adenoma was identified during a colonoscopy for endoscopic mucosal resection of a previously identified polyp. The polyp location was the rectum. The colonoscopy was negative for any signs of concurrent malignancy. This case report is the fifth case of OM in a TSA reported in English. The clinical significance of OM is uncertain, and there is limited literature describing these lesions.