In vitro modification of mesenchymal stem cells and materials via tissue engineering is useful for bone regeneration. In this paper, we briefly summarize our bone tissue engineering approach. It is also known that RNA interference (RNAi) can regulate cell proliferation as well as differentiation cascade. Recently, our study using siRNA demonstrated that bone matrix formation by osteoblastic cells can be inhibited by certain types of siRNA. These findings can show that the proliferation/differentiation of the cells used in regenerative medicine could be regulated by siRNA.