We treated T1 rectal cancer in three patients with synchronous colorectal cancer by transanal endoscopic microsurgery (TEM) before performing a radical operation for the second lesion. On pathological examination, all rectal specimens resected by TEM showed cancer invasion within the submucosal layer, while the margins of the specimen were completely free of cancerous tissue. Few complications were encountered with either the TEM for the rectal lesions or the succeeding radical operation for the second lesions. When patients present with synchronous colorectal cancer, including T1 rectal cancer, local excision of the rectal lesion via TEM can help to improve the patient's quality of life without affecting the curability of the disease.