The scaffolds for stem cell-based bone tissue engineering should hold the ability to guide stem cells osteo-differentiating. Otherwise, stem cells will differentiate into unwanted cell types or will form tumors in vivo. Alginate, a natural polysaccharide with great biocompatibility, was widely used in biomedical applications. However, the limited bioactivity and poor osteogenesis capability of pristine alginate hampered its further application in tissue engineering. In this work, a bone forming peptide-1 (BFP-1), derived from bone morphogenetic protein-7, was grafted to alginate polymer chains to prepare peptide-decorated alginate porous scaffolds (pep-APS) for promoting osteo-differentiation of human mesenchymal stem cells (hMSCs). SEM images of pep-APS exhibited porous structure with about 90% porosity (pore size 100-300 m), which was appropriate for hMSCs ingrowth. The adhesion, proliferation and aggregation of hMSCs grown on pep-APS were enhanced in vitro. Moreover, pep-APS promoted the alkaline phosphatase (ALP) activity of hMSCs, and the osteo-related genes expression was obviously up-regulated. The immunochemical staining and western blot analysis results showed high expression level of OCN and Col1a1 in the hMSCs grown on pep-APS. This work provided a facile and valid strategy to endow the alginate polymers themselves with specific bioactivity and prepare osteopromoting scaffold with enhanced osteogenesis ability, possessing potential applications in stem cell therapy and regenerative medicine.