The effect of increasing nano-sized β-tricalcium phosphate (β-TCP) content on the biological performance of polylactic acid (PLA) composite scaffold was investigated by in vitro degradation and in vivo model of heterotopic bone formation.Nano-sized β-TCP was prepared by wet grinding method, PLA/nano-sized β-TCP scaffold with increasing β-TCP (0-50wt %) contents were fabricated by freeze-drying method.The degradation behavior was carried out by determining the microstructure, the change of pH, weight and comprehensive strength in 26 weeks of hydrolysis.The study in vivo was performed by cutting the composite scaffold contain0,10,30,50% β-TCP and pure β-TCP into blocks(Smm × 5mm × 3mm), and then implanting into subcutaneous tissue of back in rabbits after loading recombinant human bone morphine protein-2(rhBMP-2), each rabbit received 4 samples.The in vitro results indicated a marked pH buffering effect as nano-sized β-TCP filler increased, however, comprehensive strength of composite scaffolds decreased significantly.On the other hand the findings in vivo demonstrated that increasing percentage of nano-sized β-TCP to PLA scaffolds enhanced their osteoconductivity.Composite scaffold containing 50% β-TCP possessed a similar biological performance to pure β-TCP in terms of osteoconductivity, but scaffold containing 30% β-TCP exhibited better mechanical properties, which can meet the demand of bone repair in load-bearing site.This supports the potential future application of PLA/30n-β-TCP scaffold as ideal scaffold for bone tissue engineering.