A new poly(amino acids)/calcium sulfate (PAA/CS) composite was synthesized by melt polycondensation from a biodegradable PAA copolymer based on 6-aminocaproic acid and the bioactive CS. Its degradability, biocompatibility, bioactivity, and osteoconductivity were evaluated in vitro and in vivo, using phosphate buffer solution soaking test, MG63 adhesion test, and bone defect model repair test, respectively. The PAA/CS composite exhibited a much lower degradation rate than the CS, as 21.6 % of weight loss after immersing in phosphate buffer solution for 5 weeks. Moreover, the pH value of local environment restored to neutrality condition after a sharp drop in the first week. The MG63 cells adhered well on the surfaces of PAA and PAA/CS plates with their filopodium and lamellipodium, and displayed great osteogenic differentiation competence. The bone defect model repair test revealed that the composite could be intimately incorporated with the surrounding bone without causing any deleterious reaction. Radiological and histological evaluation indicated the PAA/CS granules were capable of guiding new bone formation and had a much slower degradation rate than the CS. In conclusion, the PAA/CS composite is expected to be a new bone graft material for its favorable bioactivity and biocompatibility and reasonable degradability.