Numerous studies with rodent cells and animal models indicate that noggin inhibits osteogenesis by antagonizing bone morphogenetic proteins (BMPs); however, the effect of noggin on osteogenesis of human cells remains ambiguous. This study aims to examine the effects of noggin suppression on viability and BMP-2-induced osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (MSCs) in vitro. Noggin expression in human MSCs was suppressed by noggin-specific small interfering RNA (siRNA), and viability of human MSCs was determined by measuring the mitochondrial dehydrogenase activity, cellular DNA content and protein amount. The BMP-2-induced osteogenic differentiation of human MSCs was assessed by analyzing the expression levels of several osteoblastic genes, enzymatic alkaline phosphatase (ALP) activity and calcification. Our study showed that noggin suppression significantly decreased human MSC metabolism and DNA content on Days 3 and 6, and decreased total protein amount on Day 14. Noggin suppression also reduced the expression levels of osteoblastic genes, ALP, integrin-binding sialoprotein (IBSP), muscle segment homeobox gene (MSX2), osteocalcin (OC), osteopontin (OPN), and runt-related transcription factor-2 (RUNX2). Significantly decreased enzymatic ALP activity in noggin-suppressed group was evident. Moreover, noggin suppression decreased calcium deposits by BMP-2-induced osteoblasts. Collectively, this study showed that noggin suppression decreased viability and BMP-2-induced osteogenic differentiation of human MSCs, which suggests that noggin is stimulatory to osteogenesis of human MSCs. J. Cell. Biochem. 113: 3672–3680, 2012. © 2012 Wiley Periodicals, Inc.