Previously, we designed and synthesized a new NF-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), and found that racemic DHMEQ inhibited cytokine secretion and phagocytosis by cells of the macrophage cell line RAW264.7. In the present research, we looked into the effect of optically active (−)-DHMEQ on the NO production, inflammatory cytokine secretion, and prostaglandin secretion in mouse bone marrow-derived macrophages (BMMs). We also studied the effect of (−)-DHMEQ on the differentiation of macrophages. DHMEQ inhibited lipopolysaccharide (LPS)-induced NF-κB activation. It also inhibited the expression of inducible NO synthase (iNOS) and NO production induced by LPS. Using enzyme-linked immunosorbent assays, we showed DHMEQ to inhibit LPS-induced secretion of IL-6 and TNF-⍺. It also inhibited COX-2 expression and prostaglandin E₂ production and secretion. It did not inhibit the phagocytosis of fluorescently labeled Escherichia coli by BMMs treated with LPS, unlike in the case of RAW264.7 cells. Next we examined the effect of the inhibitor on M-CSF-induced differentiation of bone marrow cells to macrophages. DHMEQ showed no effect on the differentiation in terms of reactive oxygen species production and F4/80 expression. However, although BMM incorporated oxidized LDL to give rise to foam cells, the (−)-DHMEQ-treated bone marrow cells did not take up oxidized LDL. Taken together, our data show that (−)-DHMEQ inhibited LPS-induced activation of BMM in terms of NO and cytokine secretion, but its effect on phagocytosis differed between BMMs and RAW264.7 cells. We also found that the functional differentiation into macrophages was inhibited by (−)-DHMEQ.