Lung metastasis is frequent in rectal cancer patients and has a poor prognosis, with an expected three-year survival rate of about 10%. Though western medicine has made great strides in the curative resection of liver metastases, resection of lung metastases has lagged far behind. Many preclinical studies have suggested that herbal treatments block metastasis, but few clinical studies have addressed this topic. We present the case of a 57-year-old Asian male with lung metastases from rectal cancer. He first underwent resection of the primary lesion (stage IIA, T3N0M0) and six cycles of adjuvant chemotherapy. Unfortunately, lung metastases were confirmed about one year later. Palliative chemotherapy was begun, but his disease continued to progress after three cycles and chemotherapy was halted. The patient was exclusively treated with herbal medicine—standardized allergen-removed Rhus verniciflua stokes extract combined with Dokhwaljihwang-tang (Sasang constitutional medicine in Korea). After seven weeks of herbal medicine treatment, the lung metastases were markedly improved. Regression of lung metastases has continued; also, the patient's rectal cancer has not returned. He has been receiving herbal medicine for over two years and very few side effects have been observed. We suggest that the herbal regimen used in our patient is a promising candidate for the treatment of lung metastases secondary to rectal cancer, and we hope that this case stimulates further investigation into the efficacy of herbal treatments for metastatic colorectal cancer patients.