Tissue engineering requires biopolymer scaffolds with compressive strength. Bioglass produces the compressive strength required of new scaffolds, and ionized Bioglass improves cell proliferation and differentiation. Ionized Bioglass contains phosphorous, sodium, calcium, and silicon ions, but the contributions of single ions or ion complexes to the cellular effects of Bioglass have not been determined. Here, we examined the effect of silicon on cell growth and differentiation. Culture medium containing 2, 4, 6, 8, and 10 μM silicon ions was produced in a chemical neutralization reaction by mixing a sodium silicate solution and hydroxychloride, and human adiposederived stromal cells (ADSCs) were cultured in the silicon-containing medium. Cell growth was followed for 9 daysin culture, using a Cell Counting Kit-8 assay. Osteogenic differentiation was examined by alizarin red S staining and RT-PCR for osteogenic genes at 10, 20, and 30 days of culture. The proliferation of human ADSCs cultured in medium containing 2 or 4 μM silicon was significantly greater than that of ADSCs in the control medium. Differentiation of human ADSCs was increased by supplementation of the differentiation medium with 2 μM silicon. This work demonstrates that 2 μM silicon accelerated proliferation and osteogenic differentiation of human ADSCs.