Lung cancer is one of the most common malignancies worldwide. In 2022, there were approximately 1 060 600 newly-diagnosed cases globally. Uncommon metastatic sites of lung cancer include the pancreas (5%-10%), gastrointestinal tract, kidneys, heart, skin (more common in small cell lung cancer). Among these, lung cancer metastasis to the seminal vesicle is extremely rare and prone to being missed or misdiagnosed. This paper reports a case of a patient presen-ting with dysuria and prostate enlargement: Ultrasonography and enhanced CT of the abdomen and pelvis showed a mass in the right seminal vesicle, and enhanced CT of the chest showed a space-occupying lesion in the upper lobe of the right lung. Pathological examination of a puncture biopsy of the right lung lesion confirmed adenocarcinoma. Based on positive immunohistochemical markers (TIF-1 and Napsin), it was diagnosed as primary lung adenocarcinoma. Pathological examination of a puncture biopsy of the seminal vesicle mass confirmed poorly differentiated adenocarcinoma,and immunohistochemical markers were negative for CA125, CK7, PSA, and CK20, but positive for TIF-1 and Napsin, suggesting lung cancer metastasis to the seminal vesicle. Based on comprehensive examinations, the patient was finally diagnosed with stage Ⅳ lung adenocarcinoma. Molecular targeted therapy with 125 mg of icotinib tablets was administered, and ¹²⁵I seeds were implanted in both the lung and seminal vesicle lesions under CT guidance for radiotherapy. Follow-up of two months showed no progression of the lesions. This case report enriches the spectrum of metastatic sites of lung cancer and highlights the need to further summarize the clinical characteristics and prognosis of patients with seminal vesicle metastasis from lung cancer.