Objective:To detect the expression of human interleukin-33 (IL-33) in glioma and study its effects on invasion of human U251 glioma cells. Methods:Immunohistochemistry was performed to detect IL-33 protein expression in 16 normal brain tissues and 86 patients with different grades of gliomas. Transwell assay was conducted to study the effect of IL-33 on invasion of U251 glioma cells. Western blotting assays were performed to investigate changes in NF-κB expression and its phosphorylation status after IL-33 treatment. Results:IL-33 protein expression was significantly higher in glioma tissues compared with normal brain tissues (54.65% vs 6.25%,P < 0.001). The expression of IL-33 in low-grade (WHO Ⅰ and Ⅱ) glioma and high-grade(WHO Ⅲ and Ⅳ) glioma was 17.4% and 68.3% (P < 0.001),respectively. IL-33 enhanced U251 cellular invasion (P < 0.05) in vitro,and the protein expression of NF-κB was increased (P < 0.05). Conclusion:IL-33 is frequently overexpressed in glioma tissues,and may contribute to glioma cell invasion by up-regulation of NF-κB phosphorylation.