K-ras gene mutation is commonly seen in lung adenocarcinoma. Cigarette smoking is thought to be an important reason for K-ras gene mutation. Studies have reported that K-ras mutations can influence the subtyping and prognosis of lung adenocarcinoma. Recently, the techniques to detect K-ras mutation have been continuously improved, greatly promoting the detection sensitivity of K-ras mutations, even in tissues with small amount of tumor component. Emerging data showed that K-ras mutation can induce primary resistance of lung adenocarcinoma to tyrosine kinase inhibitors (TKIs) and decrease the efficacy of chemotherapy. Therefore, K-ras mutation has attracted considerable attention as a target for diagnosis and anticancer therapy. In this review, we summarize recent studies on K-ras mutations in lung adenocarcinoma, and discuss the development, diagnosis, and treatment of lung adenocarcinoma.