Oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC), a component of minimally modified low-density lipoprotein (MM-LDL), induces production of pro-inflammatory cytokines and the development of atherosclerotic lesions. We tested the hypothesis that OxPAPC alters the expression, phosphorylation, and localization of tight junction (TJ) proteins, particularly occludin, a transmembrane TJ protein. OxPAPC reduced total occludin protein and increased occludin phosphorylation in dose (10 to 50 µg/mL) and time-dependent manners in bovine aortic endothelial cells (BAEC). OxPAPC decreased occludin mRNA and reduced the immunoreactivity of zonula occludens-1 (ZO-1) at the cell-cell contacts. Furthermore, OxPAPC increased the diffusive flux of 10 kDa dextran (Pd) in a dosedependent manner. Superoxide (O₂^-.) production by BAEC increased approximately 2.0-fold after exposure to OxPAPC. Also, enzymatic generation of O₂^-. by xanthine oxidase/lumazine and hydrogen peroxide (H₂O₂) by glucose oxidase/glucose increased occludin phosphorylation, implicating reactive oxygen species (ROS) as modulators of the OxPAPC effects on occludin phosphorylation. Superoxide dismutase (SOD) and/or catalase blocked the effects of OxPAPC on occludin protein content and phosphorylation, occludin mRNA, ZO-1 immunoreactivity, and Pd. These findings suggest that changes in TJ proteins are potential mechanisms by which OxPAPC compromises the barrier properties of the vascular endothelium. The OxPAPCinduced disruption of TJs, which likely facilitates transmigration of LDL and inflammatory cells into the subendothelial layers, may be mediated by ROS.