Abstract: A new kind of biocomposite of dicalcium phosphate (DCP)/four element poly (amino acid) copolymer (PAA) was prepared by using polymerization in situ for bone repair, and its composition and structure were characterized by XRD and IR. The in vitro bioactivity and degradability of DCP/PAA composite were determined by using simulated body liquid (SBF) and Tris-HCl solution, respectively. The results show that the interactions exist between the inorganic and organic phase of the DCP/PAA composite. The polymerized reaction time has significant effects on the mechanical strength of PAA and DCP/PAA composite, and the viscosities of PAA increases with the increase of the reaction time, so the compressive strength is improved. The DCP/PAA composite has good bioactivity because the apatite could be formed on its surfaces after soaking into SBF, and the newly formed apatite is calcium deficient apatite with the Ca/P atom ratio of 1.59. The DCP/PAA composite could be degradable in the Tris-HCl solution, and intrinsic viscosities of PAA have effects on the degradation of the biocomposite. The pH value of the solution decreases slightly after the composite soaking into Tris-HCl solution at initial stages, but it is stable around 7.0~7.2 after 4 weeks later.