Human adipose tissue-derived mesenchymal stem cells (hADSCs) have therapeutic potential, including the ability to self-renew and differentiate into multiple lineages. Understanding of molecular mechanisms of stem cell differentiation is important for improving the therapeutic efficacies of stem cell transplantation. In this study, we determined the role of nuclear factor of activated T cells (NFAT5) in the osteogenic differentiation of hADSCs. The down-regulation of NFAT5 expression by the transfection of a specific siRNA significantly inhibited osteogenic differentiation of hADSCs and decreased the activity of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-${kappa}B$) promoter without affecting their proliferation and adipogenic differentiation. The inhibition of NFAT5 expression inhibited the basal and Tumor Necrosis Factor ${alpha}$ (TNF-${alpha}$) induced activation of NF-${kappa}B$, but it did not affect TNF-${alpha}$-induced degradation of the $I{kappa}B$ protein. These findings indicate that NFAT5 plays an important role in the osteogenic differentiation of hADSCs through the modulation of the NF-${kappa}B$ pathway.