OBJECTIVE： To prepare epirubicin-loaded PLGA microspheres and study its in vitro antitumor activity. METHODS： Using PLGA as carrier， epirubicin-loaded PLGA microspheres were prepared by using emulsification-solvent evaporation method. The morphology of microspheres was observed by TEM； the distribution of particle size was determined by laser granularity distribution measuring instrument； the content of main component was determined by UV spectrophotometry. The drug-loading amount and entrapment efficiency were calculated， and accumulative release rate （Q） was investigated by in vitro release test within 10 d. The proliferation inhibitory rates of prepared microspheres and epirubicin to human breast cancer MCF-7 cells were detected by MTT assay. RESULTS： The particle size， drug-loading amount and encapsulation efficiency of epirubicin-loaded PLGA microspheres were （175.2±16.8） μm， （8.6±1.3）％ and （46.7±8.6）％（n＝7）； Q4 h， Q24 h and Q10 d were 27.8％， 41.7％ and 92.3％， respectively. Compared with epirubicin， epirubicin-loaded PLGA microspheres could prolong inhibitory rate of epirubicin to MCF-7 cells for 96 h （48 h inhibitory rate of epirubicin was 96.7％， 96 h proliferation inhibitory rate of Epirubicin-loaded PLGA microspheres was 99.3％）. CONCLUSIONS： Epirubicin-loaded PLGA microspheres are prepared successfully， and show good in vitro sustained-release effect and antitumor activity.