Mimosine, which is a natural plant amino acid present in the Leucaena genus, is able to induce hypoxia-inducible factors (HIFs). Previous evidence has indicated that HIF regulates angiogenesis-osteogenesis coupling in bone metabolism, and it has previously been reported that mimosine inhibits prostaglandin (PG)F-2 alpha-induced osteoprotegerin (OPG) synthesis without affecting interleukin-6 (IL-6) production in osteoblast-like MC3T3-E1 cells. In addition, PGE(1) has been demonstrated to induce OPG synthesis via activation of p38 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in these cells, and PGE(1) stimulates IL-6 production via the activation of protein kinase A. In the present study, the effects of mimosine on the PGE(1)-stimulated synthesis of OPG and IL-6 were investigated in osteoblast-like MC3T3-E1 cells. The concentrations of OPG and IL-6 were measured using relevant ELISA kits. OPG mRNA was measured by semi-quantitative reverse transcription polymerase chain reaction. The phosphorylation of p38 MAP kinase and SAPK/JNK was analyzed by western blotting. Mimosine significantly reduced PGE(1)-induced release of OPG and OPG mRNA expression levels without affecting the release of IL-6. In addition, deferoxamine, which is also a normoxic HIF inducer, significantly inhibited PGE(1)-induced OPG release and OPG mRNA expression levels; however, it had little effect on IL-6 release. Furthermore, mimosine and deferoxamine failed to affect PGE(1)-stimulated phosphorylation of p38 MAP kinase or SAPK/JNK. These results strongly suggest that normoxic HIF inducers attenuate PGE(1)-stimulated OPG synthesis without affecting IL-6 production in osteoblasts.