The blood brain barrier has important roles for physiological and pathological state in the brain. The molecules involved in barrier function have been identified. Now we can analyze these molecules by genomics and proteomics methods. The blood brain barrier is also called neurovascular unit which is composed of brain capillary endothelial cells, astrocytes, pericytes, neurons and microglia. They closely interacted with each other for the development and maintenance of blood brain barrier functions. In this review I will summarize some basic concepts and recent new findings about blood brain barrier：structure and function, neurological diseases, proteomics method, in vitro experimental system, and enzyme replacement therapy for lysosomal storage diseases/mucopolysaccharidosis.