Serum amyloid A (SAA), a major acute-phase protein, has potent cytokine-like activities in isolated phagocytes and synovial fibroblasts. SAA-induced proinflammatory cytokine gene expression requires transcription factors such as NF-κB; however, the associated epigenetic regulatory mechanism remains unclear. Here we report that Jmjd3, a histone H3 lysine 27 (H3K27) demethylase, is highly inducible in SAA-stimulated macrophages and plays an important role in the induction of inflammatory cytokine genes. SAA-induced Jmjd3 expression leads to reduced H3K27 trimethylation. Silencing of Jmjd3 expression significantly inhibited SAA-induced expression of proinflammatory cytokines including IL-23p19, G-CSF and TREM-1, along with up-regulation of H3K27 trimethylation levels on their promoters. Depletion of Jmjd3 expression also attenuated the release of proinflammatory cytokine genes in a peritonitis model and ameliorated neutrophilia in SAA-stimulated mice. Finally, we observed that Jmjd3 is essential for SAA-enhanced macrophage foam cell formation by oxidized LDL. Taken together, these results illustrate a Jmjd3-dependent epigenetic regulatory mechanism for proinflammatory cytokine gene expression in SAA-stimulate macrophages. This mechanism may be subject to therapeutic intervention for sterile inflammation and atherosclerosis.