Aim : Several injectable materials have been used in the application of osteogenic bone substitute; however, nothing has won universal acceptance. This study was performed to investigate whether chitosan-alginate gel/MSCs/BMP-2 composites are potentially injectable materials for new bone formation. Material and Methods : The composites were injected into the subcutaneous space on the dorsum of the nude mouse to investigate whether new bone would be tissue engineered in the mouse. The composites were examined histologically over a 12-week period. Results : The composites implanted in the mouse were able to tissue engineer new bone, and the newly formed bone consisted of trabecular bone and calcified bone matrix. Conclusions : The present study shows that chitosan-alginate gel/MSCs/BMP-2 composites have the potential to become real injectable materials for new bone formation.