Purpose: The current research was conducted to investigate the efficacy and safety of pemetrexed given continuously as a basement agent for first-, second- to third line chemotherapy of patients with metastatic lung adenocarcinoma. Patients and Methods: Patients with metastatic lung adenocarcinoma who were diagnosed in Jiangsu Cancer Hospital and Research Insitute, were enrolled. All received pemetrexed 500 $mg/m^2$ (intravenous; on day 1), and another chemotherapieutic agent every 3 weeks until disease progression, or intolerable toxicity. Then the patients were changed to a second line chemotherapy that was still based on pemetrexed 500 $mg/m^2$ and another chemotherapeutic agent differing from the first line example, until disease progression, or intolerable toxicity. When third line chemotherapy was needed, pemetrexed 500 $mg/m^2$ and another new chemotherapeutic agent were combined until disease progression. Evaluation of efficacy was conducted after two cycles of chemotherapy using the Response Evaluation Criteria for Solid Tumors. Toxicity was recorded according to NCI Criteria for Adverse Events version 3.0. Results: From January 2010 to September 2013, 15 patients were enrolled. Their median age was 56 years (range 43 to 77 years). Eight patients were male and 7 female. Five patients (33.3%) achieved PR, while 6 patients (40.0%) remained stable, no CR on first line; and 1 PR (7.7%), 5 stable (38.5%) were recorded when pemetrexed was ordered in second line; 5 patients (41.7%) were stable after pemetrexed was combined in third line; no complete response was observed. Main side effects were grade 1 to 2 neutrophil suppression and thrombocytopenia. Other toxicities included elevated transaminase and oral mucositis, but no treatment related death occurred. Conclusions: Pemetrexed continuously as a basement agent from first-, second- to third line chemotherapy is mildly effective in treating patients with metastatic lung adenocarcinoma with tolerable toxicity.