Nano-hydroxyapatite (n-HAP) surface-grafting poly(L-lactide) (g-HAP) was synthesized by ring-opening polymerization of L-lactide (L-LA) using stannous octoate as initiator and n-HAP as co-initiator under microwave irradiation. An optimal reaction condition was obtained as follows: temperature of 140 °C, irradiation time of 45 min and microwave power of 50 W. The products were characterized by FTIR, TGA, x-ray scattering and particle size analysis. Results showed that the feeding ratio of nn-HAP：nL-LA had a significant influence on the grafting percentage of g-HAP. With increasing the nn-HAP:nL-LA feeding ratio from 1:50 to 1:400, the grafting percentage of g-HAP increased correspondingly from 14.91% to 35.88%. The g-HAP particles showed a smaller size than that of pristine n-HAP, suggesting that the grafted poly(L-lactide) segment facilitated to prevent the g-HAP particles from aggregating.