Xanthohumol (XN), the principal prenylated flavonoid from the hop plant, an additive that contributes bitterness and flavor to beer, is known to be a potent phytoestrogen. Although XN has been identified as a chemopreventive agent and as an anti-infective agent, its effects on bone are unknown. In the present study, the effects of XN on osteoblast differentiation and function were determined by analyzing the activity of alkaline phosphatase (ALP), an osteoblast marker, and the regulation of RUNX2, a master gene of osteoblast differentiation, in a mesenchymal stem cell line. XN upregulated ALP activity and the expression of osteogenic marker genes. Additionally, XN increased the expression and transcriptional activity of RUNX2. To determine which signaling pathways are involved in the osteogenic effects of XN, we tested the effect of inhibitors of kinases known to regulate RUNX2. Enhancement of the transcriptional activity and expression of RUNX2 were inhibited by treatment with a p38 and an ERK inhibitor. These findings suggest that XN stimulates osteoblast differentiation by activation of RUNX2 via mechanisms related to the p38 MAPK and ERK signaling pathway. Regulation of RUNX2 activation by XN may be an important therapeutic target for osteoporosis. (C) 2011 Elsevier Inc. All rights reserved.