Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that belongs to the interleukin-6 family and is expressed by multiple tissue types. This study analyzed the effect of LIF on osteoblast differentiation using primary murine bone marrow stromal cells (BMSCs). Colony-forming unit-osteoblast formation by BMSCs was significantly suppressed by LIF treatment. To clarify the mechanism underlying the LIF suppressive effect on osteoblast differentiation, we analyzed the downstream signaling pathway of LIF. LIF/signal transducer and activator of transcription 3 (STAT3) signaling induces the expression of suppressor of cytokine signaling 3 (SOCS3). SOCS3 knockdown experiments have previously demonstrated that short-hairpin SOCS3-BMSCs reversed the LIF suppressive effect. Our results demonstrated that LIF suppresses osteoblast differentiation through the LIF/STAT3/SOCS3 signaling pathway. J. Cell. Biochem. 115: 1262–1268, 2014. © 2014 Wiley Periodicals, Inc.