Objective:To study the relationship between the expression of YKL-40 and clinicopathologic characteristics and prognosis in small cell lung cancer (SCLC). Methods:The expression of YKL-40 in 105 samples of SCLC tissues and 40 samples of para-cancerous tissues were examined by immunohistochemistry. Results:The expressions of YKL-40 in cancer tissues and para-cancerous tissues were 72.4% and 22.5%,respectively(both P < 0.01). The expression of YKL-40 was not associated with gender,age and smoking,but associated with clinical stage and lymph node metastasis (both P < 0.05). Median overall survival (OS)of SCLC patients was 16.3 months. Median OS in patients with YKL-40 expression was 12.4 months,which was shorter than that in patients without YKL-40 expression(25.6 months),and there was statistically differences (P < 0.05). Univariate analysis showed that clinical stage and the expression of YKL-40 were related to the prognosis of SCLC patients,while multivariate analysis showed that YKL-40 was an independent prognosis factor of SCLC patients. Conclusion:YKL-40 may be a molecular marker to predict the relapse,metastasis and prognosis of SCLC patients.