Polylactide grafted starch (starch-g-PLA) was successfully synthesized via anionic swollen grafting polymerization. The swelling of starch was proved effective to facilitate the grafting reaction. The product with grafting percentage up to 376 % was obtained when optimized the experimental condition. The structure of grafted product was confirmed by Fourier transform infrared spectra and nuclear magnetic resonance spectroscopy. The modified starch has favorable thermal stability below 200 A degrees C according to derivative thermogravimetric analysis. The thermal property of the starch-g-PLA attested that the grafted products have great potential melt blending with PLA and starch.