The purpose of the present study was to synthesize a new composites scaffold containing poly(γ-benzyl-L-glutamate) modified hydroxyapatite/(poly (L-lactic acid)) (PBLG-g-HA/PLLA) and to investigate their in vitro behaviour on bone mesenchymal stromal cells (BMSCs). The results demonstrated that BMSC proliferation was significantly increased on PBLG-g-HA/PLLA scaffolds after 3 and 7 days post seeding when compared to PLLA and HA/PLLA scaffolds. The in vitro osteogenic differentiation also favoured the composite PBLG-g-HA/PLLA scaffolds when compared to controls by significantly increasing Runx2, ALP or osteocalcin mRNA expression as assessed by real-time PCR. The results illustrate the potential of PBLG-g-HA/PLLA scaffolds for bone tissue engineering applications. And the in vivo testing further confirms the PBLG-g-HA/PLLA scaffolds’ potentioal for healing critical bone defects.