BACKGROUND: Atherosclerosis is the main underlying cause of most cardiovascular diseases, and monocyte migrating to the vascular wall and subsequently differentiating into macrophage are critical steps in the process of atherosclerosis. The goal of this study was to clarify the effect of oleoylethanolamide (OEA) on monocyte migration and subsequent macrophage formation in the vascular wall. METHODS: We studied OEA in two monocyte-migrating systems in vitro: one was a single cell system whereby monocytes were exposed to OEA directly; the other was a co-culture system whereby monocytes were exposed to OEA-treated macrophages. The effect of OEA on macrophage content in the vascular wall in vivo was measured in apolipoprotein E (apoE)-/- mice by CD68 immunohistochemistry. The protein and mRNA expressions with OEA treatment were examined using western blot and real-time PCR. RESULTS: Interestingly, OEA possessed dual-directional regulation of monocyte chemotaxis in vitro, with a stimulatory effect in the single cell system and a suppressive effect in the co-culture system. And OEA restrained macrophage deposition in the vascular wall of apoE-/- mice. The underlying mechanism of OEA suppressing monocyte migration in the co-culture system was that OEA increased phosphorylation of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα) level, and decreased phosphorylation of signal transducer and activator of transcription 3 (STAT3) and monocyte chemoattractant protein-1 (MCP-1) level in macrophages, which was reinforced by the in vivo experiment. CONCLUSIONS: OEA restrains excessive macrophage formation in the progressive lesion by inhibiting MCP-1 production of the existent macrophages through the AMPK/PPARα/STAT3 pathway.