In this article, collagen modified polylactide (CPLA) was synthesized by means of graft modification, and its structure was confirmed by FTIR and FITC-labeled fluorescence spectra. Subsequently, the performance of CPLA was characterized with hydrophilicity test and degradability test. After that, the aspirin sustained release microspheres of the synthetic copolymers were prepared via the emulsion-solvent evaporation technique, followed with its measurements of morphology, size, and encapsulation efficiency. Finally, the controlled release properties of the obtained microspheres were investigated. The results showed that the aspirin sustained release microspheres exhibited well-defined morphology with smooth spherical surface, with average size of 3.990 m and encapsulation efficiency of 51.83%. Furthermore, compared with aspirin-loaded PLA microspheres, at the initial 32 h, the drug release was faster for aspirin-loaded CPLA microspheres favored by its increased hydrophilicity, and then the drug release was slower than that of PLA microspheres because the NH2 group on the introduced collagen inhibited acidic autocatalytic degradation. The results suggested that CPLA showed a great potential as particles for drug delivery. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013