β-tricalcium phosphate (β-TCP)/collagen composites are in the limelight for their biomedical applications. It is believed that joint status of β-TCP particles with collagen fibrils plays key roles in both osteoconductivity and biodegradability of composites. In this work, the influence of acidity during synthesis on the joint status between nano-sized β-TCP particles and collagen fibrils is investigated. The composites are characterized by X-ray diffractometer and Field Emission Scanning Electron Microscope. The results show that the joint status of nano-sized β-TCP particles with collagen fibrils in the composites depends on the acidity in collagen suspensions. A desired joint status with obvious disassembled collagen fibril, good particle dispersion and strong boding between the particles and the fibrils could be obtained when acidity of the collagen suspension is pH 2.