Liver X receptors (LXRs) are nuclear receptors that play an essential role in lipid and cholesterol metabolism. Emerging studies indicate a potential function for LXRs in regulating dendritic cell (DC)-dependent immune responses; however, the role of LXRs in DC differentiation is largely unknown. Here, we report that LXRα regulates the differentiation of mouse GM-CSF-derived DCs. Activation or overexpression of LXRα significantly enhanced myeloid DC differentiation from mouse bone marrow (BM) cells, while siRNA-mediated knockdown of LXRα suppressed DC differentiation. In addition, we demonstrated that LXR agonist-programmed DCs showed an increased capacity for stimulating T-cell proliferation. Mechanistic studies showed that activation of LXR could inhibit the phosphorylation of STAT3 and downregulate the expression of its target, S100A9, an important negative regulator of myeloid DC differentiation. We also found that Histone deacetylase (HDAC) inhibition interfered with the effect of LXR on STAT3 signaling via acetylation of STAT3. Chromatin immunoprecipitation assays confirmed that LXR activation and HDAC inhibition balanced the recruitment of STAT3 to the S100A9 promoter, which involved distinct post-translational modifications of STAT3. In conclusion, our observations demonstrated a novel role for LXRα in GM-CSF-derived DC differentiation and revealed the underlying mechanism.