Adult stem cells hold great promise for use in tissue repair and regeneration. Recently, adipose tissue-derived stem cells (ADSCs) were found to be an appealing alternative to bone marrow stem cells (BMSCs) for bone tissue engineering. The main benefit of ADSCs is that they can be easily and abundantly available from adipose tissue. However, our prior study discovered an important phenomenon that BMSCs have greater osteogenic potential than ADSCs in vitro and epigenetic regulation plays a critical role in runt-related transcription factor 2 (Runx2) expression and thus osteogenesis. In this study, we aimed to improve the osteogenic potential of ADSCs by histone deacetylase inhibitor sodium butyrate (NaBu). We found that NaBu promoted rat ADSC osteogenic differentiation by altering the epigenetic modifications on the Runx2 promoter.