Biodegradable beta-tricalcium phosphate (beta-TCP)/poly (lactide-co-glycolide) (PLGA) composites were synthesized by in situ polymerization with microwave energy. The influence of the beta-TCP content in beta-TCP/PLGA composites on the molecular weight, crystallinity, microstructure, and mechanical properties was investigated. As the molecular weight of composites decreased, the beta-TCP content increased up to 10 wt%, while further raising of the beta-TCP content above 10%, the molecular weight increased with increasing beta-TCP content. This behavior may be ascribed to the superheating effect or nonthermal effect induced by microwave energy. It was found that the bending strength and Young's modulus of the beta-TCP/PLGA composites were proportional to the molecular weight of PLGA. The bending strength of the beta-TCP/PLGA composites ranged from 18 to 38 MPa, while Young's modulus was in the range from 2 to 6 GPa.