Abstract: Objective: To investigate the immunohistochemical and ultramicroscopic features of blood -brain -barrier in the metastatic tumor tissue and its clinical meaning. Methods: With immuno-histochemistry staining, CD34、F-!、S-100、GFAP、NF、NSE、SYN and MBP were detected in tumor tissue which were resected from 16 patients with brain metastasis and 16 with glioma. Meanwhile 4 metastatic tumors and 2 gliomas were observed under the electron microscope. Results: CD34、F-! were richly expressed both in the metastatic tumor and glioma tissues, which indicates the foundation of new blood vessels; on the other hand S-100、GFAP、NF、NSE、SYN and MBP, markers of nervous tissue, were rarely expressed in metastatic tumor tissue, which indicates that there is no fundamental structure of blood-brain-barrier neurogliar membrane. Just the same as those in their primary lesions, the ultra-microscopic characters of metastatic tumors include that endothelium vacuolate, the conjunction of endothelium cells do not always tightly, and the basilar membrane is slightly thinner than that of glioma, besides there is no neurogliar foots around the blood capillary. Conclusion: Neuroglia, the basic integrant of blood-brain-barrier is defective in brain metastatic tumor tissue, thus there is no blood-brain-barrier existing in brain metastatic tumor lesions.