This study aimed to compare the efficacy of 131I therapy between elderly and non-elderly patients with lung metastasis of differentiated thyroid cancer (DTC). Thirty-eight patients diagnosed with lung metastasis of DTC were divided into elderly group (60-80 years old; 17 cases) and non-elderly (33-59 years old; 21 cases). All patients received 131I therapy following the total thyroidectomy. After six months, the overall treatment efficacy, pulmonary function, peripheral blood indexes and salivary gland function were evaluated. The adverse reactions of treatment were observed. Results showed that, the remission rate in non-elderly group was 85.73%, which was significantly higher than 52.92% in elderly group (P<0.05). The maximum voluntary ventilation in non-elderly group was significantly higher than that in elderly group both before and after treatment (P<0.05). After treatment, the white blood cell and platelet levels in non-elderly group were significantly higher than those in elderly group, respectively (P<0.05). After treatment, the uptake indexes and secretion ratio of parotid glands and submandibular glands in non-elderly group were significantly higher than those in elderly group, respectively (P<0.05). The short-term adverse reactions in elderly group were severe than non-elderly group, and no obvious chronic adverse reaction occurred in each group. 131I therapy is an effective method for non-elderly patients with lung metastases of DTC. It is also has relatively satisfactory efficacy for elderly patients, but when applying, the effects on pulmonary function, peripheral blood indexes and salivary gland function should be paid more attention.