The effect of tricalcium phosphate (TCP) as heterogeneous nucleating agent on the degree of crystallinity, mechanical properties and degradation behavior of a random copolymer poly(L-lactic-co-glycolic acid) with monomer mole ratios of 85/15 (PLLGA85/15) was investigated by XRD, differential scanning calorimetry (DSC), SEM, and studying the tensile properties and degradation properties. The results indicate that addition of TCP can improve the degree of crystallinity, but the tensile strength decreases. The in vitro degradation behavior was investigated. The changes in the water uptake, mass loss, pH value, surface morphologies and thermal property after degradation indicate that the degradation of the annealed materials is enhanced but the degradation rate of the composite materials slows down, which is the results of two factors. The first is the process of annealing, which can enhance the degradation. The second is TCP, which is alkalescent, delays the degradation rate.