The analytical electron microscopy (AEM) was employed to observe the intratissuelar distribution of polysorbnte 80 coated nanoparticles in brain with copper chlorophyll (CC), and a safe and cheap pigment was used as a marker. AEM analyses show that some nanoparticles are located at the wall of the microvasculum in brain, while others are distributed around the microvasculum in brain. These results may support that T- 80 coated nanoparticles cross the BBB through mechanisms of endocytosis or transcytosis.