Cinnamaldehyde is a flavor isolated from the bark of Cinnamomum cassia Presl and exerts anti-inflammation effects in various diseases. In our study, we investigated the protective effects and the potential mechanism of cinnamaldehyde on atherosclerosis (AS) by using a high fat diet (HFD)-fed ApoE^−/− atherosclerotic mouse model. Here, we found that the serum LDL-C, TG and TC levels were elevated and the HDL-C level was decreased in HFD-fed ApoE^−/− mice. Cinnamaldehyde treatment significantly decreased inflammatory cytokine (TNF-α, IL-6, NO and MCP-1) overproduction and the serum lipid level. Meanwhile, cinnamaldehyde increased the HDL-C level and down-regulated the activity of lipid peroxidation product MDA in serum. Moreover, cinnamaldehyde reduced the atherosclerotic plaque area in ApoE^−/− mice. Furthermore, cinnamaldehyde reduced matrix metalloproteinase-2 (MMP-2) expression and attenuated the high phosphorylation level of IκBα and p65 NF-κB. Overall, our study indicates that cinnamaldehyde may achieve the anti-atherosclerotic effect via the IκB/NF-κB signaling pathway.