━━ Background. Granulocyte colony-stimulating factor (G-CSF)-producing tumors are known to have a poor prognosis, and the efficacy of ROS1 tyrosine kinase inhibitors (ROS1-TKIs) in treating ROS1 fusion genepositive G-CSF-producing non-small-cell lung cancer has not been reported. Case. A 56-year-old male patient presented with a rapidly progressing mediastinal tumor and an abnormally high white blood cell count. The diagnosis was lung adenocarcinoma (cTXN3M1c, stage IVB). Serum G-CSF levels were elevated. Due to the rapid progression, we started carboplatin, paclitaxel, bevacizumab, and atezolizumab without awaiting the results of gene mutation testing. However, he experienced progressive disease (PD) after two courses. Subsequently, he was administered cisplatin, pemetrexed, and bevacizumab, but PD occurred again after two courses. After confirming ROS1 fusion gene positivity and starting entrectinib, the dyspnea improved the next day, and 1.5 months later, computed tomography showed shrinkage of the tumor. PD occurred three months after starting entrectinib, and we switched to crizotinib. The tumor shrank rapidly again. Conclusion. ROS1-TKIs may be effective, even for ROS1 fusion gene-positive G-CSF-producing tumors with a poor prognosis.