Abstract: Objectives To evaluate the feasibility of using CellSearch and Circulating Tumor Cell Kit（Epithelial）to detect and count the malignant tumor cells in cerebrospinal fluid （CSF） from the lung cancer patients with leptomeningeal metastasis （LM）. Methods Twenty patients with obvious clinical symptom due to LM of lung cancer and 1 patient without LM were enrolled in this study. A total of 10~15 mL of CSF were colleted with the first-time lumbar puncture. 5~7.5 mL of CSF were used to detect the number of malignant tumor cells by CellSearch method. 5~7.5 mL of CSF were used to find the tumor cells by conventional cytology. 2 mL of CSF were used for CSF routine biochemistry analysis. Results Malignant tumor cells in the CSF were found in all 20 patients with suspected lung cancer LM by CellSearch technology. The tumor cells were found in 12 patients （60%） by CSF cytology method. Malignant tumor cell was either negative in the patient as negative control. Comparison of CellSearch technology and conventional cytology technology was statistically significant（P=0.008）. Conclusion The CellSearch technology seemed superior to conventional technology in terms of finding malignant tumor cells in CSF from the patients with suspected leptomeningeal metastasis, which might be a new reliable technology for the diagnosis of leptomeningeal metastasis in NSCLC.