Microcystins (MCs) produced by toxic cyanobacteria cause serious water pollution and public health hazard to humans and animals. However, direct molecular mechanisms of MC-LR in vascular endothelial cells (ECs) have not been understood yet. In this study, we investigated whether MC-LR induces vascular inflammatory process in cultured human umbilical vein endothelial cells (HUVECs). Our data demonstrated that MC-LR decreased HUVECs proliferation and tube formation and enhanced apoptosis. MC-LR also induced intracellular reactive oxygen species formation (ROS) in HUVECs. The MC-LR directly stimulated phosphorylation of NF-κB. Furthermore, MC-LR also increased cell adhesion molecules (ICAM-1 and VCAM-1) expression in HUVECs. Taken together, the present data suggested that MC-LR induced vascular inflammatory process, which may be closely related to the oxidative stress, NF-κB activation, and cell adhesion molecules expression in HUVECs. Our findings may highlight that MC-LR causes potential damage to blood vessels.